PDF invoice non-Latin characters

[mizu]

VirtueMart 3.8.9 10473
Joomla! 3.10.4
Multi language site, en/kr
com_tcpdf_1.0.9

I'm stuck here.
VM doesn't create a readable pdf invoice with Korean characters. Question marks instead.
I read some older threads regarding this problem, but the solutions there are outdated.

I see that the fonts Courier, Helvetica are in place (libraries/vendor/tecnickcom/tcpdf/fonts), also reinstalled com_tcpdf...
What else is there to do in order to make things work?

[GJC Web Design]

Use the Free Mono font

[mizu]

tried all 3 fonts. No success.

[mizu]

according to https://www.fontshop.com/families/helvetica Helvetica doesn't support Korean. (probably Courier, Mono neither)

I guess I have to download a suitable font first.

Done that.
Converted .ttf to .ctg.z, .z , .php and created the xml file.
The dropdown box gives me a new option now.
When trying to create the PDF i get "unexpected (T_CONSTANT_ENCAPSED_STRING) "
Kinda expected a message like this.
Which file(s) do I have to edit in order to load my alternative font?

I checked the files in tecnickcom/tcpdf/ but don't see my options here.

Anyone dealt with that matter before?