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