Your system information

• Steam client version (build number or date): 1532458786
• Distribution (e.g. Ubuntu): Arch Linux
• Opted into Steam client beta?: [Yes/No] No
• Have you checked for system updates?: [Yes/No] Yes

Please describe your issue in as much detail as possible:

When Linux distributions are installed with a different language than American English, they often do not generate the en_US.UTF-8 locale in order to save disk space and improve update time. With the recent update of Steam "improving" the user interface, however, writing non-ASCII characters is broken - an attempt results in no Unicode characters appearing, and, if Steam is running without the -nofriendsui -nochatui arguments, in warnings appearing in the console. Pasting strings with Unicode characters from other sources still works fine, though.

This is probably happening because Steam uses something similar to setlocale(LC_ALL, "en_US.UTF-8"); somewhere in the code, while setlocale(LC_ALL, ""); is probably what should be used in order to conform to the system settings.

A workaround exists, involving manually adding en_US.UTF-8 to the list of generated locales. On Arch Linux, that is done by uncommenting the line #en_US.UTF-8 UTF-8 in /etc/locale.gen and running sudo locale-gen. I don't consider that sufficient to be considered a solution, though.

This is essentially the same issue as #5586, however its author has prematurely closed it based on the workaround.

Steps for reproducing this issue:

1. Use a keymap with Unicode characters present.
2. Open Steam client.
3. Open a chat with someone.
4. Try writing a message using Unicode characters.