Thank you to Dottard for a clear and informative answer.
I agree with him that the nub (central point) of the matter is the word וּמְקַלֶּלְךָ
In BHS there is a footnote attached to this word.
Literally translated it states,
"Read with Cairo Geniza, a few (3-10) medieval Manuscripts, the Samaritan
Pentateuch, the Septuagint, the Syriac Peshitta, and the Vulgate have וּמְקַלְלֶיךָ."
The form in the footnote has the prefix "me" that is a characteristic of the pi'el part. However, we do not have the characteristic pi'el doubling of the second radical (Eccl 7:21).
If we accept that this is indeed a pi'el form, it is only the suffix that has changed from
2ms to 2mp, and the note therefore does not affect the translation substantially.
I do agree with the view that we should keep the core meaning of the original root in mind, and translate the pi'el as, "curse by treating someone dismissively, disrespectful, with contempt, etc."
This view is manifested here in the translations of ESV, NLT for example. Also refer
to Lv 19;14; 1 Sm 2:30, 3:13; 2 Sm 16:5, 19:43 in this regard.
For those readers that are not all that familiar with BH grammar, here are two relevant points.
- The waw conjunctive is in the form of a shureq because it appears in front of a labial
consonant, also known as the "BuMP" letters.
- The mem+shewa is indicative of the (active) participle in the pi'el binyan of strong
verbs. This is also the case with irregular geminate verbs (verbs that have two identical
radicals in the second and third root positions) as found here.