Can you point out a reference for this?
I can understand why it would make sense, but I've never seen any regulation with required it.
ICAO regulations do not directly apply in member countries but the member countries are required to pass legislation that implements ICAO regulations. The German law says "need to be proficient in the language or English". I don't know the equivalent French bill but I bet it does not contain the "or English" part. The Canadians mention that for French in Québec, one needs to pass the test, found it
here.
Indeed it would make French airfields in accessable to many foreign pilots even if they were fluent French speakers, simply because there is no facility to add French languange proficiency to their licence.
Imagine a Norweign pilot asking the Norweign CAA for a French Languange Proficiency test so that they could add it to their licence. It's very unlikely that they would have developed such a test, or have such an examiner.
Norwegian is not an ICAO language and while theoretically possible, the AIP would probably not declare an aerodrome as Norwegian speaking only. The same applies to German which isn't an ICAO language either (mainly because ICAO was founded in 1944 without Germany) so all aerodromes are indicated as de/en in the AIP. In France, most smaller aerodromes are indicated as fr/en during official opening hours and fr only outside business hours. Some fields are only indicated as fr.