No. The label is only a value stored on the phone to help you tell lines apart; it has no bearing on the profile, the remaining data or the plan's validity. You can change it as often as you like without consequence. What does matter is which line is assigned to carry data, and that is a separate setting.

Not directly, but it is usually about which line is assigned to data. Check that the data line is the travel plan and not your home number, confirm data roaming is on for that line, then restart the phone once. A clear label just makes those two checks faster and stops you from picking wrong while doing them.

Use whichever language you read fastest when you are in a hurry — that is the only criterion that matters. Some phones show a limited set of characters or truncate long names; if that happens, shorten the label or switch languages. What is always worth doing is putting the distinguishing word first so it survives truncation.

Just set it again — it is a device-side value and does not touch the profile. What to do at the same time is confirm the data line is still the one you chose, because a reset name sometimes comes with the system putting data back on the first line, which may be your home number.

Delete only the ones you are certain you are finished with, because a deleted profile usually cannot be reinstalled. If a plan has not expired or still holds data, rename it as belonging to a past trip instead. That tidies the list without risking something you already paid for. If you are unsure which are safe to remove, ask us first.

Yes. Where a menu sits and what it is called depend on the operating system version and the manufacturer's own customisation, so two identical models on different updates can differ. The quickest route is the search box inside the phone's settings, searching for a term about SIMs or the mobile network.