Pronunciation of ‘few’ as [ˈfjyu̯]

Solution 1:

Dutch /u/ is not necessarily the same as English /u/.

I think you may be confusing the concepts of "phoneme" (which corresponds to the adjective "phonemic") and "phone" (which corresponds to the adjective "phonetic").

A phonetic transcription, using square brackets, represents a specific physical sound. When comparing sounds from different languages, you want to use a phonetic (bracketed) transcription.

But, Wiktionary transcriptions are not phonetic. They are phonemic. (They may also have other complications, like inconsistent systems being used for different words.)

A phonemic transcription, using slashes, like /ˈfju/, doesn't directly represent the sounds coming out of someone's mouth. It represents the minimum amount of information a native speaker needs to know in order to pronounce a word correctly; the important sound contrasts in that specific language. As a non-native speaker, you can't rely on a phonemic transcription to tell you pronunciation details.

Unlike French or Dutch, the English sound system does not distinguish between the phonetic sounds [u], [y] and [yu̯]. Some speakers may very well have a phonetic [yu̯] or something similar in "few", but it is still considered by English speakers to be the same sound as in "fool" where a phonetic [u] would be more common.

The realization of the English phoneme /u/ as the phone [y] or [yu̯] is considered a type of fronting, moving a vowel sound to be pronounced further forward in the mouth.

This fronting of /u/ common in North American varieties of English, especially when /u/ comes after the palatal glide /j/ or one of the coronal consonants /n, t, d, tʃ, dʒ, s, z, ʃ, ʒ/. (I think l might also be included in this list, but I'm not sure.) You can find an illustration of where this type of fronting is common at the Atlas of North American English. The fronting is least common when /u/ is preceded by a non-coronal consonant and followed directly by /l/.

The linguist Geoff Lindsey has made some blog posts mentioning the existence of this front realization of /uː/ in "Standard Southern British", and the tendency to use a more back realization before "dark l".

Solution 2:

The [y] sound (high-front-tense-rounded vowel) doesn't usually appear in modern English. Native English speakers will usually hear [y] as if it were [u] (high-back-rounded) or [ij] (high-front-unrounded with palatal glide) , so your personal pronunciation, while slightly different from that of a native speaker, will be easily understood.