I can't find the pdf manuals for all NI applications

With respect to the above mentioned then they are already available in French, both Massive and FM8.

E.g. Massive (downloads on product page)(Check zip file All Languages) (All languages manual zip)

FM8 (downloads on product page) (French PDF manual)

Absynth 5 (legacy) (French PDF manual)

but would it be possible to have the entire komplete 14 collector edition range in French or multilanguage

Sorry , I do not have the time to spend to go through all of this for you and couldn't say how much else if any is available in French language. Kontakt 7 could possibly have a manual available in French later I don't know . but both Kontakt 6 had a French version as well as did Kontakt 5 .

Anyway , for the moment then what I can suggest is that you use the online manuals for things and then use the General resource : Native Instruments online manuals with Google Chrome and auto-translate. May not be perfect but will maybe work sort off ? E.g. Kontakt 7