Font differences with different languages on signs - prevent from changing font

Hi,

I can't figure out how to use only one font on signs.

When I use non-polish letters, I have one font:

but when I use language specific letter, the font changes:

I understand that english font doesn't have these characters, but is there any way to force english lines to use the same font as different language ones?

I tried bolding the light lines, but I don't like the effect.

Thank you.