Is there a mistranslation of definition of ignorance?

You don't know suffering. If you knew suffering, there would be no suffering.

Now, you are drowning in suffering rather than knowing suffering.

If you knew suffering, you would know the tiniest thought of clinging (upadana) is suffering.

Ignorance is the root cause of the suffering? Hmm...let's take a look.

Actually the Dhamma says: Nandī dukkhassa mūlan’ti. There are also references and translations throughout the Dhamma for attachment, desire, and delight being the root of suffering.

There is no conflict with the definition of ignorance. With ignorance dispelled, the Four Noble Truths are accepted. Now walk the path.

There might be some discussion about "depth of knowing". As practice deepens, wisdom emerges, suffering is relinquished. Indeed, we have:

Bhikkhus, true knowledge is the forerunner in the entry upon wholesome states

Notice that what is said is forerunner. Knowledge is insufficient. Practice is required. Knowledge alone is insufficient:

Knowing and seeing like this, my mind was freed from the defilements of sensuality, desire to be reborn, and ignorance

According to MN 9 (below), as long as you still have fermentation or effluents, you would still have ignorance, and vice versa (also see this question). Ignorance is a very deeply ingrained and deeply lingering fetter. You know the Four Noble Truths, but when someone threatens your life, you may get scared. So, do you really know the Four Noble Truths in such a way that it dispelled your ignorance for good?

From the origination of fermentation comes the origination of ignorance. From the cessation of fermentation comes the cessation of ignorance. .....

From the origination of ignorance comes the origination of fermentation. From the cessation of ignorance comes the cessation of fermentation.

According to SN 35.153 (below), understanding by faith, by personal preference, by oral tradition, by reasoned reflection and by acceptance of a view after pondering it, is insufficient. It must be understood by "seeing it with wisdom". Only then does it obliterate ignorance permanently.

“There is a method of exposition by means of which a bhikkhu—apart from faith … apart from acceptance of a view after pondering it—can declare final knowledge thus: ‘Destroyed is birth … there is no more for this state of being.’ And what is that method of exposition? Here, bhikkhus, having seen a form with the eye (and same applies to sound and ear), if there is lust, hatred, or delusion internally, a bhikkhu understands: ‘There is lust, hatred, or delusion internally’; or, if there is no lust, hatred, or delusion internally, he understands: ‘There is no lust, hatred, or delusion internally.’ Since this is so, are these things to be understood by faith, or by personal preference, or by oral tradition, or by reasoned reflection, or by acceptance of a view after pondering it?”

“No, venerable sir.”

“Aren’t these things to be understood by seeing them with wisdom?”

“Yes, venerable sir.”

So, how does one "see it with wisdom"?

The answer comes in SN 22.98 (below), where Ven. Khemaka briefly describes the technique of Vipassana, as the method to be used to see with wisdom, in order to uproot the deep fetters of conceit and ignorance.

"In the same way, friends, even though a noble disciple has abandoned the five lower fetters, he still has with regard to the five clinging-aggregates a lingering residual 'I am' conceit, an 'I am' desire, an 'I am' obsession. But at a later time he keeps focusing on the phenomena of arising & passing away with regard to the five clinging-aggregates: 'Such is form, such its origin, such its disappearance. Such is feeling... Such is perception... Such are fabrications... Such is consciousness, such its origin, such its disappearance.' As he keeps focusing on the arising & passing away of these five clinging-aggregates, the lingering residual 'I am' conceit, 'I am' desire, 'I am' obsession is fully obliterated."

The Buddha also confirms in SN 22.47 that when ignorance is fully overcome, the "I am" conceit would be fully obliterated:

“The five faculties remain right there, bhikkhus, but in regard to them the instructed noble disciple abandons ignorance and arouses true knowledge. With the fading away of ignorance and the arising of true knowledge, ‘I am’ does not occur to him; ‘I am this’ does not occur to him; ‘I will be’ and ‘I will not be,’ and ‘I will consist of form’ and ‘I will be formless,’ and ‘I will be percipient’ and ‘I will be nonpercipient’ and ‘I will be neither percipient nor nonpercipient’—these do not occur to him.”

I think you're right that the dhamma includes more than only the knowledge of suffering -- see pages 45-46 of Piya Tan's introducton to SN 56.11

1. Suffering -- known
2. Craving -- abandoned
3. Cessation -- realized
4. Path -- cultivated

But I don't think it's a mistranslation of avijja. I guess what's happening is:

• You can't (easily) express the the complete dhamma in a single word or sentence, so any single word or sentence (like avijja) is incomplete (not the whole truth)
• I think I read recently (though I don't remember where) that it happens in the suttas that a list (of several items) may be replaced with a single item (i.e. the first item on the list), so the first item acts as a place-holder or representative of the whole list -- so perhaps, when you read "knowledge of suffering", you're expected to also understand that to mean, "... and abandoning craving, and realizing cessation, and cultivating the path".