Hello Martin,
you can include "dojo/i18n!esri/nls/jsapi" and then in your function declare the following, where in the string translation, you define the corresponding Slovenian one.
esri.bundle.widgets.measurement.NLS_area = "translation";
esri.bundle.widgets.measurement.NLS_area_acres = "translation";
esri.bundle.widgets.measurement.NLS_area_sq_feet = "translation";
esri.bundle.widgets.measurement.NLS_area_sq_kilometers = "translation";
esri.bundle.widgets.measurement.NLS_area_hectares = "translation";
esri.bundle.widgets.measurement.NLS_area_sq_meters = "translation";
esri.bundle.widgets.measurement.NLS_area_sq_miles = "translation";
esri.bundle.widgets.measurement.NLS_area_sq_yards = "translation";
esri.bundle.widgets.measurement.NLS_length_kilometers = "translation";
esri.bundle.widgets.measurement.NLS_distance = "translation";
esri.bundle.widgets.measurement.NLS_length_feet = "translation";
esri.bundle.widgets.measurement.NLS_length_meters = "translation";
esri.bundle.widgets.measurement.NLS_length_miles = "translation";
esri.bundle.widgets.measurement.NLS_length_yards = "translation";
esri.bundle.widgets.measurement.NLS_resultLabel = "translationΜέτρησης:";
esri.bundle.widgets.measurement.NLS_decimal_degrees = "translation";
esri.bundle.widgets.measurement.NLS_latitude = "translation";
esri.bundle.widgets.measurement.NLS_location = "translation";
esri.bundle.widgets.measurement.NLS_longitude = "translation";
You can also see the following guide for your reference:
Localization | Guide | ArcGIS API for JavaScript