Hi Florent,
> 2.Tassa sattamaa dhitaa a.t.thamaaya eka.m vattha.m adaasi.
> his / seventh / daughter / [to] eighth / one / cloth / gave
> His seventh daughter gave the eighth a cloth.
I would translate as "one cloth" rather than "a cloth". In the above
sentence the function of eka.m might be to emphasize that it was *one*
cloth (and not some other number of cloths) that the man's daughter
gave her sister, or it might be to imply that it was one cloth out of
several cloths that had been mentioned earlier in the passage.
But if the meaning were "a cloth" there would be no need for the
numeral eka.m, for Pali nouns are just assumed to be indefinite unless
modified by numerals, demonstrative adjectives, relative clauses etc.
Best wishes,
Dhammanando