https://imgur.com/a/ktweN
This is what happened in my Minecraft, lines with special characters (I guess so) will change to Serif fonts.
TTFR-1.2.4-1.8.9.jar
Tested with LiteLoader + Forge
MacType Installed, Windows 7
This is normal on Windows 10.

at layoutString in StringCache.java, it lookups for support fonts for string, and it changes the font if unsupported characters were met.
comment of it in code:
/* Break the string up into segments, where each segment can be displayed using a single font */

So just change code here, the problem solved.