Learn Portuguese (Portugal): Quem me dera que ela me tivesse perdoado sem mágoa. - I wish she had forgiven me without sorrow.

The expression Quem me dera que shows a strong wish. To express a regret about a past event that did not happen, we must use the Past Perfect Subjunctive (tivesse + past participle). If you used the Imperfect Subjunctive (perdoasse), the sentence would express a present or future wish: 'I wish she would forgive me'.

What is the literal meaning of Quem me dera, and what tense is dera?

It literally translates to 'Who had given it to me'. The word dera is the simple Past Perfect (Mais-que-perfeito simples) of the verb dar. While that tense is mostly found in literature today, it survives in everyday speech in this specific set phrase to mean 'I wish' or 'If only'.

Why does the pronoun me come before the verb phrase (me tivesse perdoado) instead of after?

The word que acts as a 'magnet'. In European Portuguese, subordinating conjunctions like que pull the object pronoun (me) to the front of the verb phrase. If the que weren't there, you would normally attach the pronoun after the auxiliary verb with a hyphen: tivesse-me perdoado.

Does mágoa just mean 'sorrow', or is there a deeper nuance?