Oas Oa, aua oas Oa, sind zwoa Oa

(Feel free to correct my spelling!)

Phonetically, with English pronunciation:

Owa owa, owa owa owa, sind svowa owa

Translation from Bavarian:

One egg, and another egg, are two eggs.

I bet the monks were drunk when they thought that up.

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Also the classic English one:

Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo

Which means:

Bison from Buffalo, New York, who are intimidated by other bison in their community, in turn intimidate other bison in their community.

The Buffalo one can be constructed in any number of ways, using the 3 meanings of Buffalo.