I'd like to ask for ispell support for .po files.  .po files are
translation files as used by the gettext tools collection.  Basically
they contain the english message (msgid) and translation (msgstr)
provided by the translator, plus comments (# ):

# this is the first message
#, c-format
msgid ""
"this is a message."
msgstr ""
"dies ist eine Meldung."

# this is the 2nd message
#, c-format
msgid ""
"this is the sencond message."
msgstr ""
"dies ist die zweite Meldung."

ispell should check text after "# " (but not after "#[.,:]") and inside
the field 'msgstr' only.  Göran Uddeborg already came up with the
appended extension to po-mode.el.  I'd recommend to add something along
these lines to ispell.el (as already done for 'tex).

For testing more .po files you can find here:

    http://www.iro.umontreal.ca/contrib/po/teams/PO/