fml needs to send back language dependent error messages. How we should implement it ? (Below, just a discussion not implemation in fact.) In the case of &fml4;, &fml4; calls language dependent message converter like this: Mesg(*e, KEYWORD, DEFAULT MESSAGE, ARGUMENT); Mesg() searches the specified keyword in files under /usr/local/fml/messages/Japanese/ directory. Each file contains messages with keywords to be substituted properly. For example, the keyword not_found matches not_found entry in /usr/local/fml/messages/Japanese/kern file. "One file has one keyword" and "one file for one category, so one file contains plural entries". Hmm, which is better? I don't determine it. If you use XPG (X/Open standard), catgets(catd, set_id, msg_id, char *s); function converts the message specified by LOCALE_XXX. "s" is the default message. For example, the usage is as follows: printf(catgets(catd, 30, 4, "%s: Internal match error.\n"), progname); This function uses set 30 and entry 4 in the local definition file such as /usr/pkg/share/nls/ja_JP.EUC/PROGNAME.cat. One problem is whether we should use locale or not ? In considering CUI e.g. makefml, it is better to use locale. For example, prepare /usr/local/lib/fml/$fml_version/messages/ja_JP.EUC/kern 1: %s not found 2: %s (error number = %d) . Instead, one file for one message may be useful. Especially it is easy we can customize only one message. To try the latter case, we can prepare a lot of classes such as FML::Message::ja::KEYWORD For example, there are 200 or 300 files such as FML::Message::ja::not_found . This methods has the following problems: separete files but in contrast more customizable. locale friendly? may be no. Consider an example. In the latter case, the message module will be like this? sub not_found { my .. = @_; return <<"_EOF_" $sender is ... something ... _EOF_ } Hmm, is it good ???