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Development/Tutorials/Localization/i18n (de)


Beim Applikationen schreiben an die Lokalisation denken
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Eine breite Schar an Benutzern und Entwicklern zu erreichen erfordert, dass Ihre Software übersetzt werden kann und sich auch anderweitig an sprachliche und kulturelle Gegebenheiten desjenigen anpassen kann, der Ihre Applikation benutzt. Das ist die Aufgabe von Lokalisation und diese Anleitung leitet Sie durch die grundlegenden Schritte, Ihre Applikation lokalisierungsfähig zu machen.

Was ist Internationalisation and Lokalisation?

Internationalisation, oder i18n ('i', gefolgt von 18 Buchstaben und dann ein 'n'), bezeichnet den Prozess, Ihre Applikation so zu schreiben, dass sie in jeder beliebigen Sprache und Kultur laufen kann. Dabei müssen folgende Dinge berücksichtigt werden:

  • Textmitteilungen, die dem Benutzer mitgeteilt werden
  • Dateneingabe vom Benutzer, Dateien und anderen Quellen
  • Das Format von Datum, Zahlen, Währungen, etc.

Lokalisation, oder l10n ('l' gefolgt von 10 Zeichen und dann ein 'n') ist der Prozess, eine internationalisierte Applikation an bestimmte lokale Gegebenheiten anzupassen.

Im allgemeinen internationalisieren Programmierer ihre Applikationen und Übersetzerteams lokalisieren sie.

Warum ist das wichtig?

KDE Entwicklung findet primär in Englisch statt, da dies eine breite Entwickler- und Übersetzerschaft erreicht. Englisch ist jedoch nicht die Muttersprache der meisten Menschen auf der Welt. Tatsächlich sprechen weniger als 8% der Menschheit Englisch und weniger als 5% sprechen es als Muttersprache. Auch im Internet benutzen nur 35% der Menschen die online sind Englisch als primäre Sprache und je mehr Teile der Welt an das Internet angeschlossen werden, desto geringer wird dieser Anteil werden. Zusätzlich benutzen die meisten sprachen, alleine 9 der 10 häufigsten, nicht-ASCII Zeichen in ihrer geschriebenen Form. Daher ist es einfach zu erkennen, warum es notwendig ist, Software zu lokalisieren.

Als internationales Projekt das den gesamten Globul umspannt, ist diese Lokalisation ein wichtiges Gut der KDE Kultur. Tatsächlich entwickeln viele KDE Entwickler ihre Applikationen in Englisch benutzen jedoch ihren KDE-Desktop in der jeweils lokalisierten Version.

Übersetzbaren Code mit i18n()

To ensure your application is ready to be localized you have to follow a few simple rules. All user-visible strings in your application should be translated before they are displayed on the user's screen, exceptions to this being debugging messages, configuration keys and similar types of text data.

KDE provides the KLocale class as part of libkdecore to facilitate the technical details of localization. KLocale makes it as easy as possible for developers to make their code i18n aware, but there are some things you need to be aware of so that applications are usable in other languages and countries.

Access to a global KLocale object is provided via KGlobal::locale(). This KLocale object is created automatically by KInstance and takes care of all user i18n related settings. It is deleted automatically on application exit.

Translations are made possible by the QString i18n(const char*) method, defined in klocalizedstring.h, which you must wrap all strings that should be displayed in. The QString returned by i18n() is the translated (if necessary) string. This makes creating translatable widgets as simple as in this example:

  1. include <klocalizedstring.h>

[...] QPushButton* myButton = new QPushButton(i18n("Translate this!"));

QString's native Unicode support ensures that all translations are represented correctly. All string handling done by your application should therefore use QString.

If the string to be translated contains any non-UTF8 characters, use the utf8() method to get a char*.


The i18n() method requires that a KInstance (e.g. KApplication) has been created. For any strings that are created prior to this there is another method provided: ki18n(). This allows one to mark strings that should be translated later as such. The ki18n() will return a KLocalizedString, which can be finalized into a QString (i.e. translated for real) after the KInstance has been created, using its toString() method.

ki18n() is typically used for strings given to KAboutData, because it is constructed before the KApplication and you can use i18n() only after the construction of the KApplication. Other than these special cases, it is always safe to use i18n() if you are sure that the code will be executed after construction of KApplication or some other KInstance.

Kontext hinzufügen

There is an extended version of i18n(), i18nc() which takes two const char* arguments. The first argument is an additional contextual description of the second string which will be translated. The first string is used to find the proper corresponding translation at run-time and is shown to translators to help them understand the meaning of the string.

Use i18nc() whenever the purpose of the text might be ambiguous without further context. For example, consider a context menu in a file manager with an entry called "View" which opens a viewer for the currently selected file. In this context "View" is a verb. However, the same application also may have a menu called "View" in the menubar. In that context "View" is a noun. In the English version of the application everything looks fine, but in most other languages one of the two "View" strings will be incorrect.

Additionally, translators sometimes need extra help in understanding what the text is actually referring to during the translation process.

In the file manager example above, one might therefore write:

contextMenu->addAction(i18nc("verb, to view something", "View")); viewMenu->addAction(i18nc("noun, the view", "View"));

Now the two strings will be properly translatable, both by the human translators and at runtime by KLocale.

Use this form of i18n whenever the string to translate is short or the meaning is hard to discern when the context is not exactly known. For example:

QString up = i18nc("Go one directory up in the hierarchy", "Up"); QString relation = i18nc("A person's name and their familial relationship to you.", "%1 is your %2", name, relationship);

There is also a ki18nc("context","text") method for providing context to strings which are constructed before the KInstance. It returns a KLocalizedString, so use the toString() method afterwards to convert it into a QString.

Contexts can also be added when building forms in Qt Designer. Each widget label, including tooltips and whatsthis texts, has a "comment" attribute, which will serve the same purpose as first argument to i18nc() call.

Standard Kontext für häufige Ausdrücke

Below is a chart showing some common words and phrases in English and the context that must be used with them to ensure proper translation of them in other languages.

Standard Contexts
Phrase Context i18nc Call Example
Busy Refering to a person i18nc("A person is busy", "Busy")
Busy Refering to a thing i18nc("A thing is busy", "Busy")
Color Color mode, as opposed to Grayscale i18nc("Color mode", "Color")
Creator Refering to a person i18nc("A person who creates", "Creator")
Creator Refering to software i18nc("Software", "Creator")
Display Refering to hardware i18nc("Hardware display", "Display")
Editor Refering to a person i18nc("A person who edits", "Editor")
Editor Refering to software i18nc("Software", "Editor")
Line Refering to drawing i18nc("Draw a line", "Line")
Line Refering to text i18nc("Line of text", "Line")
Name Refering to a name of thing i18nc("A thing's name", "Name") In theme change dialog: i18nc("Theme name", "Name")
Name Refering to first name and last name of person i18nc("Person's first and last name", "Name") In KAddessbook contact edit dialog: i18nc("Person's first and last name", "Name")
No Answer to a question i18nc("Answer to a question", "No")
No Availability of a thing i18nc("Availability", "No")
(Re)load (Re)load a document, medium etc. i18nc("(Re)load a document", "(Re)load")
(Re)load (Re)start a program, daemon etc. i18nc("(Re)start a program", "(Re)load")
Title Refering to a person i18nc("A person's title", "Title")
Title Refering to a thing i18nc("A thing's title", "Title")
Volume Refering to sound i18nc("Sound volume", "Volume")
Volume Refering to a filesystem i18nc("Filesystem volume", "Volume")
Volume Refering to books i18nc("Book volume", "Volume")
Yes Answer to a question i18nc("Answer to a question", "Yes")
Yes Availability of a thing i18nc("Availability", "Yes")


Plurals are handled differently from language to language. Many languages have different plurals for 2, 10, 20, 100, etc. When the string you want translated refers to more than one item, you must use the third form of i18n, the i18np(). It takes the singular and plural English forms as its first two arguments, followed by any substitution arguments as usual, but at least one of which should be integer-valued. For example:

msgStr = i18np("1 image in album %2", "%1 images in album %2", numImages, albumName);

i18np() gets expanded to as many cases as required by the user's language. In English, this is just two forms while in other languages it may be more, depending on the value of the first integer-valued argument.

Note that this form should be used even if the string always refers to more than one item as some languages use a singular form even when referring to a multiple (typically for 21, 31, etc.). This code:

i18n("%1 files were deleted", numFilesDeleted);

is therefore incorrect and should instead be:

i18np("1 file was deleted",

    "%1 files were deleted",

To provide context as well as pluralization, use i18ncp as in this example:

i18ncp("Personal file", "1 file", "%1 files", numFiles);

Datum und Zahlen formatieren

When displaying a number to the user, your program must take care of the decimal separator, thousand separator and currency symbol (if any) being used. These symbols differ from region to region. In English speaking countries a dot (.) is used to separate the fractional part of a number, while in some European countries a comma (,) is used instead. Below is a short summary of functions that will help you format the numbers correctly, taking the local conventions into account for you.

Functions to Format Numbers
Formats a.. From a.. Function Prototype
Number String
QString formatNumber( const QString & numStr )
Number Integer, double
formatNumber( double num, 
              int precision = -1 )
Money String
formatMoney( const QString & numStr )
Money Number
formatMoney( double num, 
             const QString & currency,
             int digits = -1 )
Date String
formatDate( const QDate & pDate,
            bool shortFormat=false )
Time QTime
formatTime( const QTime & pTime, 
            bool includeSecs=false)
Date and time QDateTime
formatDateTime( const QDateTime &pDateTime,
                bool shortFormat = true,
                bool includeSecs = false )

Similar functions exist to read information provided by the user at runtime in their localized format, e.g. readNumber() or readMoney().


Applikationen zu entwickeln, die sich mit Datum und Zeit beschäftigen, zum Beispiel Kalender, ist ein sehr komplexes Gebiet. Nicht nur Zeichenketten die ein Datum oder eine Uhrzeit beinhalten müssen lokal angepasst werden, man muss auch andere Aspekte bedenken, wie zum Beispiel:

  • Welcher Dag in der Woche der erste ist (cf int weekStartDay())
  • Wieviele Monate in einem Jahr sind
  • "Ära"-basierte Kalender
  • Ob ein 24-Stunden Zeitformat benutzt wird (cf bool use12Clock())

KLocale stellt neben anderen diese Methoden zur verfügung:

Kalenderdaten Funktionen
Formats a.. From a.. Function Prototype
Date QDate
formatDate( const QDate & pDate,
            bool shortFormat=false )
Time QTime
formatTime( const QTime & pTime,
            bool includeSecs=false )
Date and time QDateTime
formatDateTime( const QDateTime &pDateTime,
                bool shortFormat=true,
                bool includeSecs=false )

Dieser Abschnitt muss verbessert werden: Bitte hilf mit, verwirrende Abschnitte zu bereinigen und Abschnitte zu reparieren die ein todo beinhalten

Mehr Informationen für verschiedene Kalendersysteme geben

Häufige Fallen vermeiden

Es gibt eine Reihe von häufigen Problemen die es unmöglich machen, eine Applikation angemessen zu lokalisieren. Im nächsten Kapitel Häufige Fehler in der Lokalisation vermeiden lernen Sie mehr darüber und wie man solche Fehler vermeidet.

Dank geht an Lukáš Tinkl, Matthias Kiefer und Gary Cramblitt für die Originalversion dieser Anleitung.

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