Portuguese and Japanese on the other hand...
There are roughly 3 main groups of European languages: Italic (or Romance as you described it) for Western Europe, Germanic which is predominantly Central Europe, Scandinavian countries and the UK; and Balto-Slavic for Eastern Europe. Generally speaking of course.
However there is still a fair amount of cross pollination even with the Germanic and Italic languages, not to mention shared characteristics (not least of all a shared alphabet) that doesn’t exist with Japonic languages such as, well, Japanese.
Like when I was trying to speak german, after just some time in France. My native language is Portuguese
There's something with those two languages in that they interfere badly.
Differences between people, or differences between cultures perhaps. Having grown up in the Netherlands I did already come across Frisian and Limburgs, which are also slightly different but if you keep reading or listening you just pick it up. So I don’t know, keep practicing I’m sure you’ll get Spanish!
For example, if you start speaking (not listening to) Frisian and Limburgs, you might find yourself throwing a few Swedish or German words in the mix.
I'm white so I'm sure this was even more confusing for him