Sync some missing entries; fix some typos; etc.

[Maikuolan]

Syncs some missing entries (not all translated yet, but all language versions should at least all have the same entries now):

• "Do not forget to turn the DEBUG mode OFF." (README-ja.md). I've tried to translate it (I'm somewhat confident in it, but checking/reviewing it is still invited).
• "If you are parsing XML files, make sure entity expansion is not enabled to avoid Billion Laughs/XML bomb via exponential entity expansion attack." (README-lo.md and README-pl.md). I haven't tried to translate those entries though (I have zero confidence in my ability to translate Lao or Polish; better to either leave it be, or let someone else try to translate those entries, I think).
• "Feel free to contribute by forking this repository ..." etc (README-pl.md). Also haven't tried to translate that.

Fixes some typos:

• Some sentences missing full stops (README-id.md, README-ja.md, README-lo.md, README-mk.md, README-vi.md, README-zh.md).
• multipart/form-data ,application/json -> multipart/form-data, application/json (README-id.md, README-lo.md, README-nl.md).
• id -> ID (README-id.md, README-lo.md, README-th.md)
• etc -> ໆລໆ (README-lo.md). (Based on examples already in the file).
• e.g. -> п.р. (README-mk.md). (Based on examples already in the file).
• e.g. -> b.v. (README-nl.md). (bijvoorbeeld...).

The etc part:

• Slightly rewords one of the original English entries (not a typo fix; just to try to improve it a little).
• Normalises some spacing (README-lo.md).

[Maikuolan]

(Review requested).

[netcode]

Thanks, merged