It will be a manual process, but perhaps much easier than you think.
For each multilanguage map, change the statement
INPUT USING 'MAPNAME'
INPUT USING 'MAPNAME&'
You choose the position of the ampersand - it must be consistent for all maps, so this may be problematic for your naming standard.
At execution time, the ampersand is changed to the user’s language code (refer to system variable *LANGUAGE).
For each map to be translated, STOW the current version with the current language code. MAPNAME becomes MAPNAME1 for English, MAPNAME2 for German, etc. Again, the position of the language code must match. Then save the map again for each language you need. Edit the new maps, changing the captions to the translated text.
See Defining the Language of a Natural Object in the Programming Guide.