"Klingons respect Kahless."
Translation:qeylIS luvuv tlhIngan.
In another question the answer to this same sentence was "qeylIS luvuv tlhIngan". Are both "tlhIngan" and "tlhInganpu'" interchangeable since they both mean "Klingons"?
That is correct.
Plural suffixes (-mey, -pu', -Du') are optional in Klingon.
qeylIS luvuv tlhIngan. must also mean "(The) Klingons respect Kahless", since the lu- prefix shows that the subject is plural -- even without a -pu' ending on tlhIngan.
It's usually clearer with the plural endings on but you can also leave them off.
The correct prefix is always required. Plural markers and pronouns are generally optional. If you leave the -pu' off of Klingon, the lu- prefix makes it clear that tlhIngan is plural in this case.
If you remove the lu- prefix, but use the -pu' suffix on tlhIngan, it will require qeylIS to be plural, since otherwise you would have to use the lu- prefix.
If you leave off the lu- and the -pu', then it could mean any of the following:
both the subject and object are plural both the subject and object are singular the subject is singular and the object is plural
But it can't mean the subject is plural and the object is singular, since that would require lu-.