I can not find a way to make a EUR deposit, can we only send crypto-currency?
They don't accept fiat deposits, but there is wire transfer for $10,000 and above.
https://support.bittrex.com/hc/en-us/articles/115000198572-USD-FIAT-and-Margin-Trading?mobile_site=true
Therefore I am wondering what if I send ripple to my bittrex account then sell them for BTC on bittrex and buy the coins I want , what do you think?
I don't use Bittrex, so I am not sure if there is an option to sell XRP for other currency in Bittrex, but if there is, you can trade XRP for other currency. You might make a better profit than XRP -> BTC -> currency_you_want. You must calculate prices and fees before going for any of the option. You can also use different exchange if Bittrex is not satisfactory when trading XRP. Good luck!