Error mosh

martin@martin-Aspire-V5-591G ~
$ mosh dev
Enter passphrase for key '/home/martin/.ssh/id_rsa':
bash: warning: setlocale: LC_ALL: cannot change locale (cs_CZ.UTF-8)
The locale requested by LC_ALL=cs_CZ.UTF-8 isn't available here.
Running `locale-gen cs_CZ.UTF-8' may be necessary.

The locale requested by LC_ALL=cs_CZ.UTF-8 isn't available here.
Running `locale-gen cs_CZ.UTF-8' may be necessary.

mosh-server needs a UTF-8 native locale to run.

Unfortunately, the local environment (LC_ALL=cs_CZ.UTF-8) specifies
the character set "US-ASCII",

The client-supplied environment (LC_ALL=cs_CZ.UTF-8) specifies
the character set "US-ASCII".

locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
LANG=cs_CZ.UTF-8
LANGUAGE=
LC_CTYPE="cs_CZ.UTF-8"
LC_NUMERIC="cs_CZ.UTF-8"
LC_TIME="cs_CZ.UTF-8"
LC_COLLATE="cs_CZ.UTF-8"
LC_MONETARY="cs_CZ.UTF-8"
LC_MESSAGES="cs_CZ.UTF-8"
LC_PAPER="cs_CZ.UTF-8"
LC_NAME="cs_CZ.UTF-8"
LC_ADDRESS="cs_CZ.UTF-8"
LC_TELEPHONE="cs_CZ.UTF-8"
LC_MEASUREMENT="cs_CZ.UTF-8"
LC_IDENTIFICATION="cs_CZ.UTF-8"
LC_ALL=cs_CZ.UTF-8
Connection to dev.tools.wmflabs.org closed.
/usr/bin/mosh: Did not find mosh server startup message.
martin@martin-Aspire-V5-591G ~
$