Is all lying considered to be 'unwholesome'?

Yes it is like killing. People say killing means having the intention to kill and killing, but if you kill without wanting to kill, then the karma of the killing is not bad. They say the same thing about lying: if you want to lie and you lie, then the karma of lying is bad, but if you lie without planning to lie, then the karma of lying is not bad. THey say all those stuff about intention and action are illustrate by the degrees of wrong-doing in the vianaya.

You must read the vinaya to know more about that https://www.accesstoinsight.org/tipitaka/vin/sv/bhikkhu-pati.html#pc-part1 https://www.dhammatalks.org/vinaya/bmc/Section0016.html

THen there are people who completely fail to understand karma and who like this loophole and go even further. They claim that: when you kill, and want kill, but you imagine that your killing is a good thing, the karma of the killing is not bad.

Same with lying: if you lie, and want to lie, but you create the fantasy that you are good person for lying, then the karma of the lie will not be bad.

At the end of the day, there is nothing good about killing and lying, whether they are intentional or not. But having the intention of killing or lying is way worse than killing or lying without wanting too. THe easiest way to avoid killing and lying is through the lack of wanting to kill and lie, so typically by respecting the 5 or 8 precepts, and this is done by ''being mindful'' so sati sampajana.

Not lying and certain duty to inform others are two things. It's probably not required to speak and it's also something to think about why taking side in cases, if even taking side for other and not hidden wished punishment.

As in regard of speaking what is not trye, good to follow Nachtflug, and in regard of not only Sila but kamma, one should not forget the third door of action, mind, that with most personal impact: wishing, agree, rejoice... with a hurtful deed is the "same" as giving signs to be done or doing it by one self. So for example wishing, out of certain aversion: "ohh, may my friend get known the bad of him, I have traced, so that they will not find together".

On the other side, if actually a case, one has the possibility to do, will not hurt himself by it, it's not wrong to report of what has been seen or heard personally and ideas should be told as "personal ideas" and not for sure. So one should be very careful in regard of telling something about others and speak only that of what is really witnessed, occation and circumstances, letting others make their own proves, not taking side or force.

[Note: this gift of Dhamma is not thought for gain, exchange, stackes or other trades for the world and should possible be removed if the space is not given for liberating purpose]

The following sutta quote may be straightforward and helpful.

From Itivuttaka 25:

This was said by the Blessed One, said by the Arahant, so I have heard: "For the person who transgresses in one thing, I tell you, there is no evil deed that is not to be done. Which one thing? This: telling a deliberate lie."

The person who lies,
who transgress in this one thing,
transcending concern for the world beyond:
there's no evil
he might not do.

I remember that during a dhamma talk of the Buddhist monk, peace activist, writer and teacher Thich Nhat Hanh, he mentioned this subject. He said that If a person is trying to find a person to kill him/her and asks you the place of this person, don't tell the truth. My opinion is this is not the "lying" that harms the humanity, this is saving a person's life from an evil being. It's actually a very wholesome action. Also informing other people about the truth of an evil person is not an evil deed either.

Lying is a widespread habit of the vast majority of humans in modern times and it is really a destructive habit. Lying actually makes a human more prone to doing evil deeds, harming others and unable to feel guilty which can be the only thing for an ordinary person that stop them doing evil deeds. Lying also make a person unable to meditate properly and it make the spirituality more difficult. So "do not lie" precept of Buddhism is very important like the other precepts. But we must become free from the limited interpretations of the Buddhist principles.

Note: But for most people lying serves the selfish/egotistical purposes which is not cool. That's why people must take the lying precept seriously-except when the exceptional life experiences happens- like "saving other beings lives" ofcourse.

Sutta. Ma. Ma. cūḷarāhulovādasuttaṃ:

"In the same way, Rahula, when anyone feels no shame in telling a deliberate lie, there is no evil, I tell you, he will not do. Thus, Rahula, you should train yourself, 'I will not tell a deliberate lie even in jest.'

The four noble truth is the opposite of lying.

It's a reason that I super trust in Pali Canons because the Noble Ones can't lie at all situations.

Although I am an ordinary, I can the witness that it is possible to speak the truth in all situations because I never lie through 12 years in Buddhism. It depends on personnal management. Actually, there has not only the lie method, so the practitioner should practice the other methods instead of the lie.

However, the noble one has at least three methods to manage the unsecured situation by the murder, etc.

1. Running away.
2. Asking the evaded question to let the listeners think of the answer by themselves. See Dha.A.4 sahassavaggavaṇṇanā Tambadathikacoraghatakavatthu.
3. Mute. or sacrifice his life to keep the truth. It's just mute until the murder tortures or kills the noble one. See Dha.A.5 pāpavaggavaṇṇanā Maṇikārakulupakatissattheravatthu.

The ordinary thinks lying is the only way, but the noble one thinks there are many ways instead of the lying to manage the unsecured situation.

Additional

In Khuddaka.A. (paramatthajo.) Sikkhāpadavaṇṇanā:

How is big of the fault from the lie?

1. In immoral animals, e.g. ant and chimpanzee, lie the small body is lesser fault than bigger because of it's required more effort to lie if both animals can understand the lie.
2. In moral animals, e.g. human and god, lie the lower wholesome skill is lesser fault than higher.
3. In the animal which has the same body and wholesome skill, lie the higher passion is more fault than the lower.

All Ariyas Can't Lie

In Sutta. Aṅ. (2): catukkanipāto Āpattibhayavaggo VoharaSutta:

250. Expressions (1st)

250. Paṭhamavohārasutta

“Mendicants, there are these four ignoble expressions (the noble one doesn't express).

“Cattārome, bhikkhave, anariyavohārā.

What four?

Katame cattāro?

Saying you’ve seen, heard, thought, or known something, but you haven’t.

Adiṭṭhe diṭṭhavāditā, asute sutavāditā, amute mutavāditā, aviññāte viññātavāditā—

These are the four ignoble expressions.”

ime kho, bhikkhave, cattāro anariyavohārā”ti.

251. Expressions (2nd)

251. Dutiyavohārasutta

“Mendicants, there are these four noble expressions. (the noble one expresses).

“Cattārome, bhikkhave, ariyavohārā.

What four?

Katame cattāro?

Saying you haven’t seen, heard, thought, or known something, and you haven’t.

Adiṭṭhe adiṭṭhavāditā, asute asutavāditā, amute amutavāditā, aviññāte aviññātavāditā—

These are the four noble expressions.”

ime kho, bhikkhave, cattāro ariyavohārā”ti.

252. Expressions (3rd)

252. Tatiyavohārasutta

“Mendicants, there are these four ignoble expressions.

“Cattārome, bhikkhave, anariyavohārā.

What four?

Katame cattāro?

Saying you haven’t seen, heard, thought, or known something, and you have.

Diṭṭhe adiṭṭhavāditā, sute asutavāditā, mute amutavāditā, viññāte aviññātavāditā—

These are the four ignoble expressions.”

ime kho, bhikkhave, cattāro anariyavohārā”ti.

253. Expressions (4th)

253. Catutthavohārasutta

“Mendicants, there are these four noble expressions.

“Cattārome, bhikkhave, ariyavohārā.

What four?

Katame cattāro?

Saying you’ve seen, heard, thought, or known something, and you have.

Diṭṭhe diṭṭhavāditā, sute sutavāditā, mute mutavāditā, viññāte viññātavāditā—

These are the four noble expressions.”

ime kho, bhikkhave, cattāro ariyavohārā”ti.