"Gtk-WARNING **: Locale not supported by C library. Using the fallback 'C' locale." on OS X

### Background information:

I use Mac OSX Yosemite.

I've installed `gtk+` using `brew install gtk+` and fixed the errors using `export PKG_CONFIG_PATH=/opt/X11/lib/pkgconfig`.

I've build my program using `make` but when I try to run it I get a warning like this:

(process:16182): Gtk-WARNING **: Locale not supported by C library.
Using the fallback 'C' locale.

##Problem: I cannot find any solutions for OS X for this particular problem.

### What I've learnt so far:

1. In this thread (

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) they suggests using: <blockquote> `ipython --pylab=wx` instead of `ipython --pylab=osx`</blockquote>
but I've got no idea how python can be related to my problem (my program is written in C - the same applies to `gtk+` I guess)

2. You can find a lot of threads on this issue like this one: ([Gtk-WARNING **: Locale not supported by C library. when starting apps from the commandline](

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)) but they mainly refer to Linux and/or Ubuntu. <br>Most of the answers use a command like this sooner or later:

sudo dpkg-reconfigure locales
But there is no `dpkg` on OS X.

The issue here is that the environment variable `LANG` is not set, because I've mixed settings for Polish and English in the *Language and Region* section in *System Preferences*.

Quoting [@KenThomases](

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) who helped me a lot with this problem:
>There's not going to be any C library locale defined for the English language in Poland (i.e. en_PL.UTF-8). That's why Terminal is not setting LANG for you in your shells, even though you have "Set locale environment variables on startup" enabled.

You can read the in-depth solution here:

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