I believe language is based on your selection when you install the program.
I'm not aware that there is a separate activation number for the German version of the program.
I'm in a sort of similar position to the OP.
When I originally purchased PR 13 (via Amazon.de I believe) I first installed it with the German language (so that my wife could also use it). It turned out that many example videos (such as on YouTube) were difficult to follow as these examples were in English).
Hence I re-installed with English language (which in fact my wife can also manage). I'm not quite sure HOW I did this (maybe with ATR's help) but certainly was with the same (original) serial number.
When I moved to PE14 I used English from the start.
Interesting, did you buy an "english serial" for PE 14?
When I bought PE13 I believe I just bought PE13 - nothing about the serial number being for a particular language.
I did not actually buy PE14 - I was having issues getting PE 13.1 to burn to BluRay & proved this to Adobe Support (& that it worked in PE 14 Trial version) & they provided me with a serial number for PE14. This worked in English & I would assume it would work if I had set PE14 up for German.
Es ist egal, wo man Premiere Elements 14 kauft.
Sofern man z.B. die englische Testversion installiert hat, bleibt nach Eingabe der Seriennummer die gewählt Sprache erhalten.
Wenn man die Sprache wechseln möchte muss man nur die Installation starten