i18n with foreign package

[Hanspeter Roth]

Hello,

I'm trying to install a foreign package with i18n with a specific
prefix. The package is icewm-1.2.8pre2 and the prefix is
/usr/opt/icewm-1.2.8pre2.
So the locale directory becomes
/usr/opt/icewm-1.2.8pre2/share/locale . Here are several language
directories. Their names are be.po, ca.po, cs.po and so forth.
Below there is de.po/LC_MESSAGES/icewm.mo for example.
But starting this icewm with LANG=de_DE has no effect. LANG=C is
used.
How can I run this icewm with the German local without copying
the icewm.mo into the public place /usr/share/locale/... ?

-Hanspeter