[Exception] Array index is out of range

I was demoing our game at EGX Berlin this weekend and got an unexpected crash (once). Checking the logs I suspect it may have been caused by I2 Localize giving me this cryptic stacktrace:

IndexOutOfRangeException: Array index is out of range.
at I2.Loc.LanguageSource.Export_Language_to_Cache (Int32 langIndex, Boolean fillTermWithFallback) [0x00000] in <filename unknown>:0
at I2.Loc.LanguageSource.SaveLanguages (Boolean unloadAll, eFileType fileLocation) [0x00000] in <filename unknown>:0
at I2.Loc.LanguageSource.UpdateDictionary (Boolean force) [0x00000] in <filename unknown>:0
at I2.Loc.LocalizationManager.AddSource (I2.Loc.LanguageSource Source) [0x00000] in <filename unknown>:0
at I2.Loc.LocalizationManager.RegisterSourceInResources () [0x00000] in <filename unknown>:0
at I2.Loc.LocalizationManager.UpdateSources () [0x00000] in <filename unknown>:0
at I2.Loc.LocalizationManager.InitializeIfNeeded () [0x00000] in <filename unknown>:0
at I2.Loc.LocalizationManager.get_CurrentLanguage () [0x00000] in <filename unknown>:0
at I2.Loc.Localize.OnLocalize (Boolean Force) [0x00000] in <filename unknown>:0
at I2.Loc.Localize.Awake () [0x00000] in <filename unknown>:0

I can't really wrap my head around what's going on here, but I guess somehow OnLocalize triggers initialization which in turn tries to update and save the dictionary data with an invalid language index. The game was running on German systems which correctly localized all content into German (after the initial crash).

Game is built with Unity 2018.1.3f1 with I2 Loc 2.8.7 and the crash occured on Windows (not sure which version).

Any help is much appreciated!

I also havn't been able to reproduce the crash, I suppose it's that kind of "heisinbug" that only occurs when you're showing your game to someone else

Thanks for replying!