For french texts, LanguageTool recognizes an ordinary space character (U+0020) or a thin space (U+2009) before ; : ! ? » and after « as a bug and suggests to substitute it with a narrow no-break space (U+202F). That’s perfectly fine.
The problem: LanguageTool doesn’t recognize a no-break space (U+00A0) before ; : ! ? » and after «. This can lead to inconsistent typografy because in the same text there can be in some places a no-break space before ; and in other places a narrow no-break space. And LanguageTool doesn’t recognize that. LanguageTool should tread a no-break space (U+00A0) in this case like an ordinary space character (U+0020) or a thin space (U+2009) and suggest to substitute it with a narrow no-break space (U+202F).
Use case: You have to compile a document from different sources. Some people give you Word files, others give you simple text files. Some of them use an ordinary space character (U+0020) before ; : ! ? », others use a narrow no-break space (U+202F) which is the default autocorrection in MS Word, OpenOffice and LibreOffice. When you put all this together in OpenOffice and correct it with LanguageTool, than the ordinary space character (U+0020) is substituted by a narrow no-break space (U+202F), but the no-break space (U+00A0) stays as it is — leading to a document who’s typografy is inconsistend.
closing old issues, we're at Github now