fix crash in fr-FR locale

[k-yle]

Closes #8673

dist/locales/fr-FR.min.json doesn't have languageNames or scriptNames, so we need to lookup these properties from the file for the base language (dist/locales/fr.min.json)

I can't add unit tests because the test suite deliberately only loads the en locale, and you can't override this for individual test cases

[tyrasd]

Thanks a lot!

A similar bug is also triggered on some other "rare" locales which don't have a base-language to fall back to. These are all locales in dist/locales which don't define any languagenames:

lij.min.json
cv.min.json
tum.min.json
lus.min.json
kbd.min.json
en-US.min.json
nso.min.json
ay.min.json
fa-IR.min.json
ba.min.json
fr-FR.min.json
kha.min.json
ts.min.json
skr.min.json
nl-NL.min.json
pa-PK.min.json
gan.min.json
ny.min.json
nr.min.json
nv.min.json
ve.min.json
jam.min.json
ss.min.json
oc.min.json
sm.min.json
pap.min.json
tn.min.json
st.min.json
dv.min.json
he-IL.min.json
tl.min.json
grt.min.json

db886f5 fixes these additional cases by using the fallback mechanism to use the language name in the respective native language, or the pure language code.