Will high blood pressure affect my pilot medical certification?
Without knowing German, it's a little difficult for me to research the LBV's website, but I found this application for Validation of a foreign airman’s licence, and one of the requirements in it is:


  Valid JAR-FCL Medical Class I or Class II 


The JAR requirements for a Class I and Class II medical, both are:


  JAR–FCL 3.135 Cardiovascular system – Blood pressure 
  
  (a) The blood pressure shall be recorded with  the technique given in
  paragraph 3 Appendix 1 to  Subpart B [at each examination]. 
  
  (b) When the blood pressure at examination  consistently exceeds 160
  mmHg systolic and/or  95 mmHg diastolic, with or without treatment,
  the  applicant shall be assessed as unfit. 
  
  (c) Treatment for the control of blood  pressure shall be compatible
  with the safe exercise  of the privileges of the applicable licence(s)
  and be  compliant with paragraph 4 Appendix 1 to Subpart 
  
  B. The initiation of [ ][medication] shall require a  period of
  temporary suspension of the medical  certificate to establish the
  absence of significant  side effects. 
  
  (d) Applicants with symptomatic hypotension  shall be assessed as
  unfit.


It looks like you will probably need to lower your blood pressure (either via diet and exercise or with medication) in order to pass your medical.  If you start taking blood pressure medication, you will need to take it for a certain period of time to make sure that there are no other side effects before they will give you a medical.  You can discuss this with a medical examiner to see how the process works there.