I've installed Mepis 6.0 and some extra packages, and after that I'm getting error with locales:

"perl: warning: Please check that your locale settings:
LANGUAGE = (unset),
LC_ALL = "en_US",
LANG = "en_US"
are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
locale: Cannot set LC_ALL to default locale: No such file or directory"

It happens after the installtion of Gimp or Inkscape, when the system removes:

g++
g++-3.3
g++-4.0
libc6-dev
libexpat1-dev
libjpeg62-dev
libstdc++5-3.3-dev
libstdc++6-4.0-dev
libungif4-dev

and after that it removes linux-kernel-headers also.

Is there any solution ?
Thanks in advance !

This is not clear enough to analise yet
You have methods in the menus to set locale , have you done that?

Yes I set my locale in system settings to en_US in MEPIS System Tweaks. But didn't help!
I put iocharset=iso8859-2 into fstab, but the problem remains. I don't know what to do.

I dont have anything in my fstab file- Take that out -where(what line ) and why did you do that?

System Configuration(Settings)->Regional->Country

Look through your menues thats what they are for

fstab tells the system which encoding to use when mounting partitions, an other OS may use a different encoding than the default, so if you created file in an other OS and the filename contains non-ascii characters, they can be encoded in 8859. But when you start your linux, without iocharset options it will use the default charset option (like utf-8).
So linux won't display your file names properly, they might contain strange characters.

Your real problem has nothing to do with this.
Its a problem with the locale of your linux.
I don't know Mepis, I'm using debian but try to reinstall(or install) package that contain locale in their names. Maybe completly removing them (purge) and then reinstalling these packages is better. As the previous poster said, also looking in the menus should fix things (but maybe something is broken in Mepis?)
These packages would probably launch:
locale-gen
Try to run this command manually.

I don't get it? Why are you having trouble installing gimp and inkscape when gimp and inkscape are in synaptic? What are the 'extra' packages that you mentioned? Did you need to enable some outside repositories? I am using 6.5 Rc1 and inkscape is there in synaptic package manager. So is gimp. You should be able to right click the program title in synaptic and choose 'Mark for installation' the rest is simple. If you still need help then you should paste your repository list in your next post for me to look at. It may have something to do with it.