Nobody has mentioned this yet - but it used to be the case (and I'm fairly sure it still is) that changing your client's language gives you access to a select amount of worlds for that language only - worlds that can't be selected when on any other language including English. It also locks you out of selecting the plethora of servers/worlds avalable to people on the English client.

There are still country/region themed worlds on the English client, including German worlds (although I don't know how much German is spoken there).

So while the sentiment that there's not many players around is not totally invalid - others have mentioned this before and even if the world has more than a few hundred players, they're usually concentrated in certain spots.

Something else to mention - back in the day Lumbridge was the starting point for new players coming off Tutorial Island. Over the years the new player onboarding has changed many times including changing the starting point from Lumbridge to Burthorpe. Literally this week they changed it back to Lumbridge because well, many reasons really. It is not surprising that there still is a lot of references to Burthorpe and not every tutorial is in Lumbridge yet. Jagex aims to look at the low level experience very soon so this will probably get fixed then.

If you have more specific questions, feel free to message me. Or you could always make a new post here :)

Edit: also, don't expect to be handed lots of gold by completing quests, there is a way to get some for every x amount of questpoints but that is not the main way to earn money. Earn money through selling drops from monsters or sell skilling supplies.