The issue appears to be similar. The localization issue may be related, but to me it happens much more often than every two days. Only today this happened twice, the difference was lower than 12 hours.

Same issue with French.

1. Set language to French and restart Steam.
2. Restart the computer or reload Steam.
3. Steam may forgot username and password. And language is full English.

I remember a much older discussion about the same issue.

The Steam client overwrites $HOME/.steam/registry.vdf with data that contains no user info:

"Registry"
{
	"HKLM"
	{
		"Software"
		{
			"Valve"
			{
				"Steam"
				{
					"SteamPID"		"0"
					"TempAppCmdLine"		""
				}
			}
		}
	}
}

I was able to "fix" this by adding the required settings and then making the file read-only:

"Registry"
{
	"HKCU"
	{
		"Software"
		{
			"Valve"
			{
				"Steam"
				{
					"language"		"german"
					"AutoLoginUser"		"djcj"
					"RememberPassword"		"1"
					"SourceModInstallPath"		"/home/djcj/.local/share/Steam/steamapps/sourcemods"
					"AlreadyRetriedOfflineMode"		"0"
				}
			}
		}
	}
}

It's weird because sometimes after an installation all this doesn't happen. Maybe it has something to do with timestamps, but I really don't know. A side-effect of having the settings file read-only may be that, if you close Steam during a download or installation it may not continue automatically after a restart. Verifying the cache of a game can help here.

I'm affected by this too. I hate it.

@Kiibakun sudo chattr +i ~/.steam/registry.vdf

But that file contains not only my language configuration, it also has "installed apps" and things. Thanks for the workaround but will not have some bad side-effect?

@Kiibakun these if you close Steam during a download or installation it may not continue automatically after a restart, or try this https://github.com/ValveSoftware/steam-for-linux/issues/5030#issuecomment-325124645

Uhm, thanks, then i'll do that, i never close steam while updating. 😄

Seems to be fixed in the Steam beta client for me.

Having the same problem on MacOS for a long time. Updated to beta, seems that it's fixed in it, selected language is now preserved between restarts.

Still having this issue on Ubuntu 16.04.3.

still relevant

Nenhuma soluçao, para este problema estou usando o Steam pelo debian 8, possuo dois computadores com o mesmo sistema operacional, e ambos com o mesmo problema com o Steam:perder o idioma, nao salvar login e senha e mais algumas coisinhas, até parece que não comprei um produto, para não darem nenhuma solução com o update

I have the exact same issue with the only difference being that my two computers run Ubuntu 16.04.3 and not Debian 8.

@ThePierrasse nota-se uma falta de sensibilidade na hora de compatiblizar a Steam para o sistema Linux e olha que nos dois usamos duas distros mais utilizadas por usuarios dos sistemas Linux

I have the same issue for Russian language.

I never again played my steam games, but I will update my steam to see if they have already solved

Since I reported this issue, I upgraded Xubuntu to 18.04 Bionic Beaver and there were a few updates on the Steam client, but this particular issue was not solved yet.

issue still exists.

Issue still happens and it's extremely annoying. Steam keeps forgetting my login info and/or language randomly.

Ubuntu Budgie 18.04 64 bits. Language set to Spanish.

Same as Leon on Ubuntu 18.04, Steam sometimes restart in English instead of my native language or worse loose my login/password...
Ubuntu 18.04 64 bits French

the problem still persists.

Kubuntu 18.04.1
i always have to change the language to portuguese (brasil) after a reboot. is really annoying.

yeah, got effected by this and it's so annoying that I'm actually here lol. I'm on ubuntu 18.04 and I want to use hungarian always.
Anyways I still love steam.

Still relevant (Linux Mint 19.1)

@ steam devs:
If this can be fixed by changing the access rights of the registry.vdf file, why don't you just do that as a temporary solution until you figured out the actual cause of this?