efektivnji
Efektivnji is not a standard term in major South Slavic languages and is generally treated as a nonstandard or misspelled form. It appears in some informal writings or regional writings, where speakers may attempt to form a comparative adjective from the stem related to “efektivni” or from the English loanword “effective.” However, in formal or standard usage, this form is typically avoided.
In standard orthography, the comparative of a stem like this is usually written as efektivniji, meaning more
For adverbs, the corresponding form is generally efektivno, meaning effectively. Speakers who wish to express efficiency
Usage notes: if you encounter efektivnji in a text, it is advisable to treat it as nonstandard