Cache user locales when they interact with the bot

[alvarogzp]

Now we only cache user locales when they perform inline queries, but there are more ways for a user to interact with the bot that we can use to perform preventive caching. These ways include:

• commands, an update added preventive caching on /start command, but it can also be added to every command or even every message received from a user

Update: it seems that telegram does not always send language_code when users send a command to the bot. It always does for inline queries, which is good for us, but this behavior can prevent caching on all user interactions.