Seed phrases or, more accurately, mnemonics¹ are not part of the protocol. Bitcoin core (bitcoind) and many full-node apps do not use them.

They provide a convenient way to represent an integer with 128 to 256 bits. Seed phrases range from 12 words (128-bit integer) to 24 words (256-bit integer).

The most common type of seed phrase has 24 words.

These words are not random. They are chosen from a list of 2048 words in various languages, such as 'apple ', 'banana ', 'car ', 'dog ', etc. By construction, a seed phrase depends on the language. You cannot translate a seed phrase in English to Spanish by translating each word.

The seed phrase contains a checksum. Every combination of 24 words, even if they all come from the correct list, is not a valid seed.

In conclusion, you should always write a seed phrase precisely as given.