No matter what you do, do not use the IP address to set the language.
Google is very annoying about this - when I enter a new place, I get google in the local language and script. This is especially annoying, especially in southeastern Croatia.
The worst offender is Microsoft. When you try to purchase software, your servers constantly switch languages depending on your location and in many cases make it impossible to pay by credit card, as addresses and postal codes, etc. They are checked in the local format, and not where your credit card was issued (By the way, the first four digits of the credit card number indicate the issuing institution, which is tied to a specific country, therefore, it is not necessary to launch a scientific rocket to develop a postal code format in the UK, not six-digit German postcode.
James anderson
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