In many countries, the government finds it important for people to properly return to society after their imprisonment. This will reduce the chance they will commit another offence.
However, when people are imprisoned in a foreign country, a proper return to society will be more difficult. That is why it is possible to serve a sentence in their own country. This is called a transfer of sentences.
In the Netherlands the international transfer of sentences is governed by two acts:
WETS (for countries in the European Union)
See Information sheet about the WETS here
WOTS (for other countries)
See Information sheet about the WOTS here