I know there is
onboard available but I can't find any setting for changing font in preferences. Though it has ability to choose custom-layout but I've to make it.
Something like: On windows, the on-screen keyboard has this option:
So-that I can set font and watch new layout:
As explained if I've fonts of another/different language than it is very useful to work by means of this layout according to font!
Note: this is not actually changing language or input-sources but only fonts
So, I am looking for FOSS that provides feature of changing fonts.