There’s a few English-language options if your son is really interested in pursuing his education in Germany.
One would be Bachelor’s degrees entirely taught in English. There aren’t very many of them, but here’s one: https://studium.hs-ulm.de/de/Seiten/Studiengang_CTS.aspx?SearchCategory=Bachelor;
Another set of undergraduate degree programs is aimed specifically at international students who may be intending immigrants. The degree program starts out in English and then transitions to German in higher semesters, with concurrent German language courses required along the way. Here’s an example: https://www.htw-dresden.de/de/fakultaet-elektrotechnik/studium/electrical-engineeringelektrotechnik.html
Here’s a search engine for “international” degree programs taught at German universities that you may find useful: https://www.daad.de/deutschland/studienangebote/international-programmes/en/
The last cheap option would be a “Studienkolleg.” These are year-long transition programs offered to international applicants who don’t quite meet the requirements for admission to a public university, particularly students who haven’t completed calculus or lack German language proficiency. The curriculum for an intending engineering student would include German as a foreign language, calculus, and a review of high school physics, chemistry and computer science (with an emphasis on subject-specific language skills). Since all courses are taught in German, admission to a Studienkolleg does require low-intermediate (B1) German skills, but that’s significantly less than what’s required for regular admission to a university (B2 or C1).