Prepositional phrase >>to talk against<<

• 'Talk against' means to publicly express opposition, criticism, or disagreement regarding a person, policy, or idea. It involves voicing negative opinions or arguments to counter a particular viewpoint, often in a debate or to highlight faults.

But the source of the above would be queried or worse by some contributors.

The fact is, the string (probably better analysed† as verb + preposition rather than multiword verb / phrasal verb) is far less common (as Mark Foskey says) than 'speak against'. The only relevant reference I have found is as a definition rather than being defined:

• Complain To:

Today, let us study the phrasal verb ‘Complain To’, which we often find in common parlance. We shall discuss its meaning and use in a number of sentences. Though it is not a phrasal verb in the conventional sense, it is used with this specific preposition.

Meaning —

• To talk against something or someone before an authority.

[Atmaja Bandyopadhyay, Department of Law, University of Calcutta; Quora]

[In all honesty, the definition leaves a lot to be desired; the complements of 'against' and 'to' here are of course quite different. However, the required string is taken as acceptable.]

So the strings picked out below

• Joan spoke against the new regulations.
• Ali talked against the way the legislation against immorality was gradually weakening.
• Tom complained to the board about several aspects of his treatment.

are all 'not phrasal verbs in the conventional sense'

(†ie are analysed as [verb] + [preposition] {then + prepositional; complement}

rather than [verb + particle] + [noun phrase], ie not as multiword verbs.

But they do select for specific prepositions.

'Talk against ...' is acceptable, but not exactly idiomatic; 'speak against' would normally seem the more natural choice.

"Spoke against" is far more common, but "talked against" is sometimes used.

"If you talked against the government, you’d be imprisoned or killed."

• "If you spoke against the government, you’d be imprisoned or killed."
• "If you railed against the government, you’d be imprisoned or killed."

The first sentence expresses opposition, while the second sentence specifically conveys a tirade—more emotive, vehement or denunciatory.

The phrasing talking against isn't idiomatic; related expressions include:

• talking past someone — talking to them in such a way that one is unable to understand or comprehend what is being said or speaking in a way that ignores, excludes, or fails to engage with them (perhaps by addressing different points or even assumptions);
• (in literary criticism) reading against a text — interpreting it in opposition to its surface meaning or even to its authorial intent.