Following a discussion with siebrand on IRC, here is some reference material on how TranslateWiki works with MantisBT's i18n.

• Mantis currently uses https://github.com/wikimedia/mediawiki-extensions-Translate/blob/master/ffs/FlatPhpFFS.php
• configuration for that is in https://github.com/wikimedia/translatewiki/blob/master/groups/MantisBT/MantisBT.yaml
• mantis could probably use the MediaWiki core FFS with some small updates, but we really need to get rid of the constants [1].

[1] referring to the error code constants at the bottom of strings_english.txt

FFS = File Format Support

Only a single branch can be the recipient of the translations at a given point in time.

The switch to a new branch assuming no changes in the format, is trivial and can be done within 1 day.