You could use a full fat client eg Thunderbird or Evolution, Outlook or whatever and use that to do some filtering through an IMAP connection. However that does rather negate the convenience.
If you use a mass email provider, you get a rather generic experience. How on earth are Goog n co supposed to work out what you consider to be spam or UBE? I imagine that you get some basic filters (naughty words and a few IP deny lists) and a tokenizer n bayesian classifier that does the really hard work. Keep tagging the crap mail as spam and after a while it should learn, that for you: German - probably unwanted, Cyrillic - probably unwanted etc. Unfortunately you don't get to see under the hood/bonnet to understand what is actually going on.
I recommend that you stick with manually notifying spam for a while and see if that works - you need a lot of samples. If Goog allows you mark ham then use that too but I suspect they implicitly mark a mail as ham if you don't mark it as spam. When I say a lot of samples, I think you need at least 200 ham and 200 spam samples minimum, ideally 500 each and the more the better. Moving to another mass mail supplier will almost certainly not help.
You could also try another provider or DIY. Another option is something like Mimecast which you put in front of Gmail - https://www.mimecast.com/products/platform-selection/mimecas...
If you use a mass email provider, you get a rather generic experience. How on earth are Goog n co supposed to work out what you consider to be spam or UBE? I imagine that you get some basic filters (naughty words and a few IP deny lists) and a tokenizer n bayesian classifier that does the really hard work. Keep tagging the crap mail as spam and after a while it should learn, that for you: German - probably unwanted, Cyrillic - probably unwanted etc. Unfortunately you don't get to see under the hood/bonnet to understand what is actually going on.
I recommend that you stick with manually notifying spam for a while and see if that works - you need a lot of samples. If Goog allows you mark ham then use that too but I suspect they implicitly mark a mail as ham if you don't mark it as spam. When I say a lot of samples, I think you need at least 200 ham and 200 spam samples minimum, ideally 500 each and the more the better. Moving to another mass mail supplier will almost certainly not help.