Malayalam: Failed to parse (syntax error): \frac{ക}{ച}
Tamil: Failed to parse (syntax error): \frac{க}{த}

Hindi: Failed to parse (syntax error): \frac{क}{च} Also, if one keeps the code as:
then it is rendered as instead of "क्ष". This is because "क्ष" is a conjunct conjunction, i.e, क्ष = क् + ष.

Simple forms like Failed to parse (syntax error): ക also fails!

Another problem: rendering in MathML.

Given the example of the non standard text character ä (a-Umlaut). It has to be mentioned that

  • Failed to parse (syntax error): ä is no valid even though it's rendered in a way that it could be considered as correct.
  • whereas or Failed to parse (SVG with PNG fallback (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "/mathoid/local/v1/":): \text{\"a} are both valid tex input but the second input is not rendered correctly (it's supposed to look like the first input).