
This is the IPA transcription for ‘tveir’, which means ‘two’, from Wiktionary. Imagine a complete beginner bumping into this. 😀 (Beginner both in phonetics and Icelandic—RIP linguistic ambitions.)
I always try to check the exact transcription in Icelandic on Wiktionary because my ear is not yet completely trained to naturally percept, say, voiceless /n/ or /l/. I’m still bad at vowels, too, which means I suck at almost everything. Honesty is a virtue.
Today, I came across the cute [t̪v̥ei̯ːr̥] transcription while watching Ása’s banger on the weather vocabulary. If you learn Icelandic, her channel is a must, trust me.
Back to the struggling. What do all these signs mean?
‘These signs’ are called diacritics and can be found in the bottom-left part of the IPA chart.

Honestly, I’m not sure any deep comments are necessary since you have the explanation right on the chart.
Let’s just see the realization of each phoneme. In [t̪v̥ei̯ːr̥],
/t/ is dental ([t̪]),
/v/ is voiceless ([v̥]),
/i/ is non-syllabic ([i̯]),
and /r/ is the word-final voiceless [r̥]. Yeah, embrace voiceless consonants in Icelandic.
Here you have Ása’s ‘tveir’ from her video on numbers:
(My question is: why can’t we transcribe the <ei> nucleus as /ej/? What do you think?)
There are some other sounds in Icelandic that might be interesting, such as the palatal plosive [c], the velar fricative [ɣ], and the near-close near-front [ʏ] (the rounded mate of [ɪ]). Want more? This Wikipedia page might help.
That’s it for today. I just wanted to share the lovely [t̪v̥ei̯ːr̥] transcription with you—and some thoughts.
Bless.