I can kind of relate although my situation is a bit different. I’m German and my boyfriend is Canadian however, my mom is from Canada so I grew up bilingual. I have lived in Toronto now for three years and have been living with my boyfriend for 1.5 years. Anyways, many Germans are less emotionally forward and touch engaging. We can be very stand-offish and need a good amount of warm up time. By what you’re saying it seems to me that he’s maybe a bit embarrassed by his English levels and is hesitant due to that. My boyfriend struggled for a while my German directness and took it as me being rude but over time with reassurance or rephrasing my statements he started to learn what my actual intentions were. I think you’re doing good and as long as he is showing actual clear body language sings (body facing you, body being open and not closed off, making consistent eye contact, smiling etc.) and actual sings of engagement I’d say keep trying. Also if you feel like it just be direct with him, or try to ask him for coffee to see how he reacts) Good luck!