Android 10 based LineageOS not rendering Indic languages
At last I was able to add support for the language[Answering for the sake of others who might face this issue]. It seems there was some issue with the font I tried earlier( though it was looking fine in PC and was known to be working in other models of mobiles ). Steps followed

Downloaded relevant ttf and otf fonts to SD card
Rebooted to TWRP
Mount-&gt;Select System &amp; External SD-&gt;Uncheck 'Mount read-only'-&gt;Select 'Internal Storage' for mount location
Press Home( not Back ). Clieck ADvanced-&gt;Terminal
In terminal, copy the fonts to /system/fonts/ using cp command ( The copy in Advanced-&gt;File Manager also might work, but I havent tried )
Mount-&gt;UnSelect System &amp; External SD-&gt;Uncheck 'Mount read-only'-&gt;Select 'Internal Storage' for mount location
Reboot to system
Verify if font support is available by going to Settings-&gt;Language ( or browsing to a webpage with that language )

Many thanks for the support and the initial hint that this might be a font problem @Andrew