Use localization for "Sum" in Stats

[meinhart]

package Kernel::System::Stats

When using dynamic stats elements the sum row and column should be able to be localized. F.e. row column is hardcoded "Sum" and i didn´t get it working that it uses the correct translation with correct culture.

[svenoe]

Please confirm whether there is a "Translate()" missing, and add it, if so.

[stefanhaerter]

Regarding the sum row, the Translate() is indeed missing. Regarding the sum column, Translatable() is used (and seemingly does not work), but it works with Translate().

[stefanhaerter]

Closed with merging #3827