Localisation

The format of the message catalog is as follow:

 line       : '#' comment              # a comment
            | tag ':' definition       # a tag definition
            | tag '=' tag              # a link to another tag
            | '[' prefix ']'           # a prefix to append to other tags

 prefix     : tag                      # the tag to use as prefix
            | '*'                      # don't use a prefix

 definition : string                   # a string
            | string '\' definition    # with posibility of continuation '\'

 tag        : [a-zA-Z0-9_]+