Debian – How to set LC_ALL=en_GB.UTF-8 in Raspbian

There are three sets of locale settings¹:

• LANG, the fallback setting, if you haven't specified a value for a category. It's indended for users to indicate their locale in a simple way.
• LC_xxx for each category (xxx can be MESSAGES, TIME, etc.).
• LC_ALL overrides all settings. It's a way for applications to override all settings in order to work in a known locale (usually C, the default locale), typically so that various commands produce output in a known format.

So you can set LANG=de_AT.UTF-8 and LC_MESSAGES=C (C is the default locale and means untranslated; en_US is usually identical to C for messages).

However, there are two categories where I don't recommend changing the default, because it breaks a lot of programs:

• LC_COLLATE is the character collation order. It's not very useful because it only indicates how to sort characters, not how to sort strings. Tools that know how to sort strings don't use LC_COLLATE. Furthermore a lot of tools expect things like “[a-z] matches all 26 ASCII lowercase letters and no other ASCII characters”, but that's not true in most non-default locales (try echo B | LC_COLLATE=en_US grep '[a-z]').
• LC_NUMERIC indicates how to display numbers. In particular, in many languages, it makes floating point numbers use a , rather than . as the decimal point. But most programs that parse numbers expect a . and treat a , as a field separator.

So I recommend to

• either explicitly LC_COLLATE=C LC_NUMERIC=_C,
• or leave LANG unset and only set a value for the useful categories (LC_MESSAGES, LC_TIME, LC_PAPER, plus LC_CTYPE (whose value may vary depending on your terminal)).

¹ _{Plus LANGUAGE with GNU libc. If you hadn't heard about it, you're not missing much.}

You can do this using udev. Create a file in /etc/udev/rules.d with the suffix .rules, e.g. local.rules, and add a line like this to it:

ACTION=="add", KERNEL=="i2c-[0-1]*", MODE="0666"

MODE=0666 is rw for owner, group, world. Something you can do instead of, or together with that, is to specify a GID for the node, e.g:

GROUP="pi"

If you use this instead of the MODE setting, the default, 0660 (rw for owner and group) will apply, but the group will be pi, so user pi will have rw permissions. You can also specify the OWNER the same way.

Pay attention to the difference between == and = above. The former is to test if something is true, the latter sets it. Don't mix those up by forgetting a = in ==.

You have to reboot for this to take effect.

"Writing udev rules" Reference