In English, typically these are also loan plurals, where a plural can be formed with the English plural -s suffix, or as per the borrowed language. These loan plurals are particularly from Latin and Greek (i.e. they are Latin plurals and Greek plurals), largely because French, the other major source of English loan words, generally forms plurals in a similar way to English with a plural -s.
An example would be "stadium", which can be "stadiums" or "stadia".
Sometimes one form may be used more often than another. If one is very frequently used and the other infrequently used, then the infrequent form may be considered non-standard. This frequently depends on register. In academic English the Greek or Latin form is often preferred, whereas in everyday speech the Anglicised form may be preferred.
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