Bayer Leverkusen coach Xabi Alonso says the success of German clubs in European competitions has further enhanced his club’s remarkable season. Leverkusen won the Bundesliga for the first time this season and are on for a treble, with their Europa League semi-final second leg at home to Roma taking place on Thursday and a German Cup final against Kaiserslautern set for May 25. Borussia Dortmund are already through to the Champions League final on June 1 and Bayern Munich may join them. “The high level of the Bundesliga shows that what we have achieved this season has not been easy,” said the S…