In general when defining customer specific labels or texts you need to go to folder '<ECTR_INSTDIR>\customize\dictionary'. Here you can define labels or texts for every language by using the according subfolders. If you for example want to edit the English label of a context menu entry you need to open folder 'en' and edit the file 'customer.txt' that can be found inside.
ECTR Label Definition
fnc.doc.open.fast.view = Open Original Read-Only fnc.doc.open.any(edit) = Open Original for Edit / Checkout
To get an overview of the existing lables you may look into '<ECTR_INSTDIR>\basis\dictionary'. However it is not advisable to change the labels directly in the basis folder. Instead if you want to alter an existing label you should copy the line from the basis directory to the customer file and change it there. ECTR will always prioritize the customer specific labels over the default ones.
Note:
If you want to customize addon or application specific commands, you may need to escape any occurences of colon using a backslash.
ECTR addon or application label definition
fnc.add.with.macro(myaddon\:addon_MacrobasedSearch.txt) = Add Object of add-on to folder