The DefaultLg contains the English text. This file will always work with the version of Messenger Plus! it came with.
Other language files contain a small text string like
code:
CompatibilityLevel=3087
that specifies for what version they are made. If the version of Plus! you are using is newer or older then the CompatibilityLevel doesn't match and you will not be able to change the language to the one with the faulty compatibility level.
You can change the compatibility level in the .ini file yourself. For Messenger Plus! 3.40.112 BETA the compatibility level is 3106. However, although you'll be able to use the language then, note that some translations may be missing or incorrect because the language file was not made to be used with the one you are using
/ 
