Special thanks to Ulrike Fischer who provided the indirect definition with active \nfss@catcodes.
This work may be distributed and/or modified under the conditions of the LaTeX Project Public License, either version 1.3 of this license or (at your option) any later version.
Many free fonts are extensions of a basic font family with new glyphs or shapes. Sometimes they are given a new name due to license reasons or the creators preference.
The substitutefont package facilitates the task to set up a font family as substitute for another one in a specified font encoding.
Use the txtt font family from txfonts instead of CM for monospaced text (enables monospaced-bold as well as monospaced-italic):
\usepackage{substitutefont} \substitutefont{T1}{txtt}{cmtt}
CB-Fonts for Greek text in a document using Times/Helvetica/Courier: test-greek.tex, test-greek.pdf
TeX-Gyre with Cyrillic from the once included Freefonts: test-cyrillic.tex, test-cyrillic.pdf
Monospaced text in many variants with txtt: test-txtt.tex, test-txtt.pdf
References: