Permissible to Require Loan Apps in English Only?

Yes. Reg Z gives you the ability to use other languages when certain conditions are met but this is not a requirement. More often it is considered a CRA outreach effort. To allow other than English applications can impose a burden on the bank as the application goes well beyond loan approval uses. Auditors look at them, examiners, compliance, safety and soundness reviews, collectors, counsel, those perfecting security interests, etc. Accepting other than English then requires all of these people to be bilingual or have an interpreter. That can be quite a burden.

I also question the bank that offers bilingual staff, adds some documents and/or advertising in a foreign language but only opens new accounts or loans in English. From a consumer perspective, this could be done clearly or it could appear to be a bait and switch when the consumer doesn't really understand the terms they "agreed" to because the advertisement that brought them in was in a foreign language and it was explained to them in that language, but they didn't know about the fees, rates or other conditions in the actual agreement.