wxLocale AddCatalog failed

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C++

wxWidgets

I have this locale switching problem.
First of all this is my directory structure:

+ Project
--+ locale
-----+ en
--------- Project.mo
-----+ ja
--------- Project.mo
--- application.exe

This is part of my code:

wxConfigBase *cfg = wxConfigBase::Get();
lang = cfg->Read (Locale, lang);
if (lang.CmpNoCase(wxT("ja")) == 0)
{
m_locale.Init (wxLANGUAGE_JAPANESE);
}
else if (lang.CmpNoCase(_("en")) == 0)
{
m_locale.Init (wxLANGUAGE_ENGLISH);
}
m_locale.AddCatalogLookupPathPrefix(wxT("locale"));
m_locale.AddCatalog(wxT("Project"));

The problem is:
If lang is "ja" then this executes "m_locale.Init (wxLANGUAGE_JAPANESE);"
When the AddCatalog function is executed, it fails.
Though the application still operates, but the labels of the application are still english.

I don't understand why AddCatalog fails if language chosen is wxLANGUAGE_JAPANESE.