Sunday, July 13, 2014

Notes from Calligra Sprint in Deventer. Part 1: Translation-friendly code

Last weekend we had a really nice sprint Deventer, which was hosted by Irina and Boudewijn (thank you very much!). We spent two days on discussions, planning, coding and profiling our software, which had many fruitful results.

On Saturday we were mostly talking and discussing our current problems, like porting Calligra to Qt5 and splitting libraries more sanely (e.g. we shouldn't demand mobile applications compile and link QWidget-based libraries). Although these problems are quite important, I will not describe them now (the other people will blog about it very soon). Instead I'm going to tell you about a different problem we also discussed — translations.

The point is, when using i18n() macro, it is quite easy to make mistakes which will make translator's life a disaster, so we decided to make a set of rules of thumb which developers should follow for not creating such issues. Here are these five short rules:

  1. Avoid passing a localized string into a i18n macro
  2. Add context to your strings
  3. Undo commands must have (qtundo-format) context
  4. Use capitalization properly
  5. Beware of sticky strings
Next we will talk about each of the rules in details:

1. Avoid passing a localized string into a i18n macro

They might be not compatible in case, gender or anything else you have no idea about

// Such code is incorrect in 99% of the cases
QString str = i18n(“foo bar”);
i18n(“Some nice string %1”, str);

Example 1

wrongString = i18n(“Delete %1”, XXX ? i18n(“Layer”) : i18n(“Mask”))


correctString = XXX ? i18n(“Delete Layer”) : i18n(“Delete Mask”)

Such string concatenation is correct in English, but it is completely inappropriate in many languages in which a noun can change its form depending on the case. The problem is that in macro i18n(“Mask”) the word "Mask" is used in nominative case (is a subject), but in expression "Delete Mask” it is in accusative case (is an object). For example is Russan the two strings will be different and the translator will not be able to solve the issue easily.

Example 2

wrongString = i18n(“Last %1”, XXX ? i18n(“Monday”) : i18n(“Friday”))

correctString = XXX ? i18n(“Last Monday”) : i18n(“Last Friday”)

This case is more complicated. Both words "Monday" and "Friday" are used in the nominative case, so they will not change their form. But "Monday" and "Friday" have different gender in Russian, so the adjective "Last" must change its form depending on the second word used. Therefore we need to separate strings for the two terms.

The tricky thing here is that we have 7 days in a week, so ideally we should have 7 separate strings for "Last ...", 7 more strings for "Next ..." and so on.

Example 3 — Using registry values

KisFilter *filter = filterRegistry->getFilter(id);
i18n(“Apply %1”, filter->name())

// CORRECT: is there a correct way at all?
KisFilter *filter = filterRegistry->getFilter(id);
i18n(“Apply: \”%1\””, filter->name())

Just imagine how many objects can be stored inside the registry. It can be a dozen, a hundred or a thousand of objects. We cannot control the case, gender and form of each object in the list (can we?). The easiest approach here is to put the object name in quotes and "cite" that literally. This will hide the problem in most of the languages.

2. Add context to your strings

Prefer adding context to your strings rather than expecting translators reading your thoughts

Here is an example of three strings for blur filter. They illustrate the three most important translation contexts

i18nc(“@title:window”, “Blur Filter”)

Window titles are usually nouns (and translated as nouns). There is no limit on the size of the string.

i18nc(“@action:button”, “Apply Blur Filter”)

Button actions are usually verbs. The length of the string is also not very important.

i18nc(“@action:inmenu”, “Blur”)

Menu actions are also verbs, but the length of the string should be as short as possible.

3. Undo commands must have (qtundo-format) context

Adding this context tells the translators to use “Magic String” functionality. Such strings are special and are not reusable anywhere else.

In Krita and Calligra this context is now added automatically, because we use C++ type-checking mechanism to limit the strings passed to an undo command:

KUndo2Command(const KUndo2MagicString &text, KUndo2Command *parent);

4. Use capitalization properly

See KDE policy for details.

5. Beware of sticky strings

When the same string without a context is reused in different places (and especially in different files), doublecheck whether it is appropriate.

E.g. i18n("Duplicate") can be either a brush engine name (noun) or a menu action for cloning a layer (verb). Obviously enough not all the languages have the same form of a word for both verb and noun meanings. Such strings must be split by assigning them different contexts.

Alexander Potashev has created a special python script that can iterate through all the strings in a .po file and report all the sticky strings in a convenient format.


Of course all these rules are only recommendation. They all have exceptions and limitations, but following them in the most trivial cases will make the life of translators much easier.

In the next part of my notes from the sprint I will write how Boud and me were hunting down memory fragmentation problems in Krita on Sunday... :)


  1. Thank you for sharing these hints!

  2. Hello! You can better translate your strings by using a collaborative translation management platform like It can be a reliable localization tool for developers and project managers.

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