When you import a file, the language (MQL4/MQL5) is decided while you are doing that. I can't remember exactly... maybe because of the file extension of the input file or most probably by getting information about that from the embedded project information.
When you generate .mq4/.mq5 file from fxDreema, the project data is embedded at the end of that file and it looks like a big comment with letters. Then when importing, this data is read only. And in that data there is information about the language.
If you want, you can have MQL4 project, copy its blocks and paste them into a new MQL5 project. And then check that everything works, because there are few differences here and there.
