Translation sets are not deeply merged

[MaSch0212]

When registering multiple translation sets with the DynamicTranslationService while these have the same root node, the last registered set wins.

Example:
en.json for translation set "a"

{
  "menuEntry": {
    "a": "Entry for Module A"
  }
}

en.json for translation set "b"

{
  "menuEntry": {
    "b": "Entry for Module B"
  }
}

This results in "menuEntry" only having "b".