Zabbix User Interface (UI) uses GNU gettext.
The language becomes enabled in Zabbix frontend when it is at least 50% translated.
In general, UI translations are much simpler than those for documentation, but here are some things that you have to be mindful of:
UI translation strings often include numbered formatting markers such as %1$s, %2$s, etc.
If the source string contains these markers, all of them must be included in the translation string precisely as they appear in the source string, i.e., a percent symbol, followed by a number, then a dollar sign, and ending with a letter.
These markers and some other elements that need not be translated are highlighted in gray in the source string. Just click such an element to have it easily copied into the necessary place of your translation.
If a string needs plural forms, you will see three tabs above the translation text area. Make sure to switch between these tabs and add plural form translations, pressing Save for each of those.
If translation is missing for some of the tabs, this will cause an error during import to Zabbix, and incomplete translation will have to be deleted.
During Zabbix release procedure, errors in UI translations are checked for, and if any are encountered, the release process cannot continue. If errors occur in a language that Zabbix team speaks, then we will attempt to fix them. Otherwise, the troublesome translations will be deleted.