Should I be concerned about creepy letter?

Sorry if this is not the right sub, but it’s so bizarre and it was sent via RM signed for… Has anybody else received something like this?

Also not sure what the language is, Google thinks it might be Hindi? But can’t make sense of it.

I’m suspecting a single nutcase instance, as we’ve not had anything else weird like this show up in the past 6 months but a little worried it could be something else.

Any experiences, translation, or advice would be much appreciated, thanks!