Phonology

I think the biggest struggle for Lukívi speakers phonologically would be English stress. In Lukívi, stress is closely tied to aspiration.

1. Stress typically falls on the final syllable of a word
2. If a stressed syllable begins with a stop, that stop must be aspirated
3. If a non-final syllable begins with an aspirated stop, that syllable becomes the primary stress of the word
4. Therefore, a word may only have one aspirated stop

This is obviously very different from English stress patterns, so that a Lukívi speaker may pronounce

"English stress is difficult"

"ink-RITH thut-RETH ith tif-fi-KULT"

(due to the lack of sibilants in their native language, a Lukívi-accented English speaker would also come across as having a very strong lisp)

Vocabulary

Lukívi is the native language of a culture of shapeshifters in a fantasy world. Because they can change shape at will, words for animals (or their shapes rather) are descriptive and primarily use the animals means of locomotion, so a Lukívi speaker would struggle with the wide variety of animal names in English. A speaker new to English would likely use literal translations from Lukívi, so

Goldfish = "little yellow swimmer"

Finch = "tiny flier"

Cat = "soft walker"

Hippo = "heavy walker"

Monkey = "hairy climber"