Idea: Farsi and Russian both have simple list of vowel sounds and no diphtongs. Making it hard/obvious when attempting to speak english, which is rife with them and many different vowel sounds

While Persian has only two diphtongs and 6-8 vowels, Other Languages of Iran are full of them(e.g. Southern Kurdish speakers can pronounce 12+1 vowels and 11 diphtongs). I find it funny if all Iranians are speaking English with the Persian accent.

Yeh they seem to be in the same "major" cluster, although Serbian/Croatian, Romanian, Bulgarian, Turkish, Polish and Czech are all close.

Turkish and Persian seem to be the nearest neighbors.

When I went to Portugal I was struck by how much Portuguese there does sound like Spanish with a Russian accent!

Part of this is the "dark L" sound

I’d guess that the sibilants, consonant clusters, and/or vowel reduction would play a big role.

I thought I was the only one who perceived an audible similarity between Portuguese and Russian.

I am native Russian speaker, and work/visited Portugal. It definitely tricks me when not paying attention, its very similar sounding

I speak neither, and both also sound similar to me depending on the accents of the speakers.

The characteristics that make pt-PT sound similar to Russian are largely absent in pt-BR.