gnu man(1): Recognize locales with Scripts in name

gnu man(1): Recognize locales with Scripts in name

Our GNU man considered locales out of the form of xx_YY (where x is
anything except "_" and Y isn't checked) to be invalid.

However, we have valid locales like sr_Cyrl_RS which were being
rejected.  Adjust the validation code to handle these names.

It also appears that man requires a codeset to be specified, e.g.
fr_FR would be ignored but fr_FR.UTF-8 would be accepted.  I didn't
do anything about this.