The best way of organizing GeoIP on the website?

2. Depends on the relevance of the database chosen service
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4. It is possible, but still allow the user to change the site language
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For one of my recent projects I used — ipinfodb.com/ip_location_api.phppretty accurate and current database, tightened caching, that would reduce the number of requests and still works like a clock.

ipgeobase.ru/ I use this service.

There are still Russian www.ashmanov.com/tech/geo
But on Habre wrote that it didn't work — Ashmanov repented moving.

ipgeobase.ru Works only in Russia or CIS, and ipinfodb.com/ip_location_api.php working with the world, but the answers will be in English.
We yuzaem and then another if the first is not defined ask the second, it is clear to us that the one who came not from the CIS or Russia will understand the answer in English.

In debianish there is the package geoip-database, and binding for PHP package php-geoip.