> However, my dominant online language is sure to be British English
It doesn't matter. Your native language is the one you were raised with as a
child, not necessarily the one you use the most now. More importantly, as you
yourself recognize, you are not fluent or even particularly proficient in
English usage.
> Eastern memes know almost none to free software
That's where you come in. Trying to communicate about the issue in broken
English isn't going to solve the fact that the idea is not very well-known
among Cantonese-speaking circles. What can help solve that is for you to
speak about the issue, in your native language. Like I said, for now at
least, stick to the basic, basic fundamental values. Tie them in with other
values that are familiar to you. Talk about it among your peers, the people
you speak to on a daily basis.
Are you able to read and write Cantonese? If so, you can talk about it on the
Internet that way, too, in a forum and situation where the discussion is
appropriate.
In the long-term, you can focus on improving your understanding English so
you can translate https://www.gnu.org/philosophy/free-sw.html into Cantonese.
I'm sure there are probably textbooks written in Cantonese that teach
English, and there are also tons of forums and other resources on the
Internet that can help. I found this, for example:
https://www.englishforums.com/
Any of this would be very helpful to the libre software movement in the
long-term. This is a global movement, and it should include exclusive
Cantonese speakers, too.