The Verdict: Need More Info
Your case turns on evidencing German at B1. Book a placement test at a Volkshochschule to see whether you need a course or just the certificate.
Section 10 of the Nationality Act asks for B1: you can handle everyday situations and give reasons for an opinion, well short of fluency. People who have lived and worked in Germany for years are often at B1 without ever having been tested.
The usual proof is a Zertifikat Deutsch B1 or the integration course certificate. A German school leaving certificate, vocational qualification or degree is accepted instead. None of these expires.
Exemptions exist only where illness, disability or age prevents you meeting the requirement, and they are assessed on evidence. Working in English does not count.
Take the naturalisation test at the same time: 33 multiple-choice questions, pass mark 17, from a published pool.