I think you are mixing different issues here.
- For privacy reasons, media in Germany must not name certain suspects, and sometimes not certain convicted criminals. This leads to news reports like "the presumable perpetrator, Thomas A., ..." and it is (in theory) not publicly known who this "A." is.
The police and the courts know the full name, of course. And so do viewers in the courtroom. Generally speaking it is possible to watch court proceedings in Germany. In high-profile cases slots may be limited and taken by the press, and there might be high-security cases (usually the same), but for average cases one can simply show up and listen. One cannot take pictures, however.
- A criminal record may be entered into a trial. It might establish a pattern, or influence sentencing. Germany has lay judges (Schöffen) rather than an US-style jury, so there is less concern of preventing prejudice to a jury; the lay judges deliberate with the professional judges.
- Evidence from abroad may be entered into a trial.
- The German prosecution can request assistance from the police and prosecutors in other countries. That's relatively easy within the EU, more difficult for other countries.
- Other countries send information to the German police, prosecutors, and intelligence services. At times, intelligence information can be used by German agencies to judge a situation but not revealed in court, so it cannot be used in a prosecution. The agencies know about a terrorist, but they cannot prove anything without betraying this confidence.
- There are logistical and legal problems with that -- generally witnesses testify in court, where the judges judge their credibility. Witnesses can be heard by teleconference, but that is the exception.
So when the evidence is used in court, it usually becomes accessible to parts of the German public (those on the viewer's gallery of the courtroom). There are some situations where the public is excluded, e.g. where minors are involved.