change handling of locales with option -L

1- If the user provides something that "looks" like a locale
   ([a-z][a-v]_[A-Z][A-Z]*), I set LANGUAGE and LC_MESSAGES.
2- If the user provides something that looks like a language code
   ([a-z][a-v]), I set LANGUAGE.
3- Otherwise, I print an error message.

i18n/start-help/en.txt

@@ -10,6 +10,8 @@ options:
   -R      reset game
 
   -L ...  set LANGUAGE variable (ex: -L fr:it:en)
+          On non GNU systems, set the variable LC_MESSAGES
+          to a valid locale.
 
   -q      quiet: don't show information messages
   -n      black and white: don't use ANSI escape codes for color

i18n/start-help/fr.txt

@@ -10,6 +10,8 @@ options :
   -R      recommence une partie du début
 
   -L      initialise la variable LANGUAGE (ex : -L fr:it:en)
+          Pour les système non GNU, initialisez la variable LC_MESSAGES
+          avec une locale valide.
 
   -q      mode silencieux : n'affiche pas les messages d'information
   -n      mode noir et blanc : n'utilise pas les séquences ANSI

start.sh

@@ -66,20 +66,7 @@ do
       RESET="TRUE"
       ;;
     L)
-      if locale | grep "LANGUAGE" >/dev/null
-      then
-        export LANGUAGE=$OPTARG
-      else
-        if locale -a | grep -qx "$OPTARG"
-        then
-          export LC_MESSAGES=$OPTARG
-        else
-          echo "Unknown locale: '$OPTARG'." >&2
-          echo "You can run 'locale -a' to get a list of all locales installed on your system." >&2
-          locale -a | grep "$OPTARG" && echo "The above locales might be relevant..." >&2
-          exit 1
-        fi
-      fi
+      export LANGUAGE="$OPTARG"     # only works on GNU systems
       ;;
     X)
       echo "$(gettext "Error: this option is only available from an executable archive!")" >&2