Sometimes, a native speaker of a given language receives their higher education through another language; say, a native English speaker whose higher education takes place in France, through French.
This will often mean that that person has somewhat limited vocabulary in their native language within certain more technical fields.
Is there a word in English that describes this kind of proficiency with ‘technical gaps’ in the vocabulary?
This is a superb question. For single-word-requests, it is a social norm that, if there is - in fact - no such single-word, someone has to provide the full, correct answer to the literal single-word-request question. I will now do that:
There is no such single word in English, which means, "the surprisingly limited vocabulary in the native language of a native language speaker who has, as it happens, spent a considerable amount of time (particularly say while pursuing higher education) in a second language region."
I know many, many people precisely as you describe. It's a great question.
{Note too that a sibling phenomenon is wherein: entirely 100% native English speakers, who have crap English spelling, because their parents moved to Germany or Japan during the years they were, say, 13 to 20, for example.}
Now, setting aside single-words. (Answer: "there is no such single-word.")
I've always struggled even trying to find a phrase for this.
I think I once said something like "X has typical eurotrash vocabulary!" or perhaps "eurotrash language skills". For me "eurotrash language skills" would mean the person is amazingly good at speaking a number of languages, but, suffers precisely the word-less quality you describe.
Similarly phrases may be "expat language base" or "expat language skill" or "X has a typical expat vocabulary" or "X has a typical expat-family vocabulary" and so on.
I hope this helps.
BTW regaring the "number of languages you speak" it's always worth reading Douglas Hofstadter.
Note too that there's a phrase common in many countries "You're worth as many people, as languages you speak." You could perhaps make a play on this if discussing the concept you raise, OP.
Well, the opposite of proficiency is deficiency, which is a single word, but must be qualified with "in X".
For example, "My daughter learned math in French immersion, so she has a deficiency in English math terminology."
Following the insightful discussion from @Joe Blow, I agree on the impasse (i.e. the question is so pin-point/situational that an English single-word couldn't handle it) and want to present an etymological approach.
To start, we associate "speaking" with "ability (and even mastery/authenticity) in the realm of languages. Subconsciously, to speak English implies the basic literacy from which one can write as well. Voice works as human medium of speech and serves as root word in both
(an aggregate "finesse" or prowess, which builds up with conversations and day-to-day "experience" in addition to academic efforts, on level of relevance and richness word choices can be)
and
(technical/occupational sense, acquired via higher education and expertise)
It is derived from vocem in Latin that interestingly captures verbal aspects as well as "sentence" and "word." That notion suggests that this so-called language proficiency actually comes down to verbal/colloquial (which is arguably harder to master given its intrinsic nature — we say "native speaker," rather than "native writer") v.s. written/scripted forms of linguistics and having a balance/versatility between them.
For example, Jon could excel at writing a tactful French essay on the Renaissance; meanwhile, he may find it awkward to orate and scrutinize on Picasso's influence on abstract art in English (and vice versa). While the topics themselves are related, he may find equivocal aspects of difficult while communicating in "voice" or static "letters" of ideas on paper.
On that note, "double-edged tongue/pen" comes to mind.
