https://bugzilla.redhat.com/show_bug.cgi?id=1427550
--- Comment #9 from Shriramana Sharma samjnaa@gmail.com --- (In reply to Seshadri N from comment #2)
Missed one important step:
1a. Copy 9 Lohit Devanagari and 2 Arial Glyphs and Paste into Lohit Tamil font at the respective places.
IANAL but I think Arial glyphs should not be copied to Lohit fonts because of copyright issues. Use an OFL-compatible source font for borrowed glyphs and make sure they are at least stylistically acceptable to be in line with Lohit Tamil style.