The solution I contrived to translate into Esperanto Esperanto untypical sounds is the following. Esperanto as more than 90% pronounce it is actually a slavic language by its phonetic system. The five regular vowels are a as is father or car, open e as in bet or bare, open o as in more or cot (British), closed i as in pique or technique, closed u as in rule or prune.
A sixth vowel common to all slavic languages (though not phonemic in all) is hard i pronounced as i in English will or y as in Russian Tchernobyl, which is an open-lipped intermediate between i and u as open-lipped e is intermediate between a and i and open-mouthed o is intermediate between a and o. This sound, though not official, is in reality unescapable in Eo as it is the elementary short sound between two consonants when a double consonant is being pronounced with the effort of distinguishing them neatly as in lit-kovro : just observe your own mouth and hear the sound and there is a slight y after lit : litykovro whether you like it or not.
That sound is likewise happening any way as it is the least effort sound in slavic languages when consonant clusters appears without any vowel indication, and this is traditionally said to happen with Esperanto too, in such compound words as retestr-subskribo. The hyphen can at any place stand for that intermediate vowel having a rather hushed sound pronounced with the mouth closed but the lips rather lax. This sound can help distinguish the parts of a lengthy compound is the same way the hyphen distinguishes them visually. It can be used exactly in the same way as in Serbo-Croatian or Czech to give dangling consonants a neutral leaning sound like in Brno or Trst (Triesta) which both could be written Br-no, Tr-sto in Eo, though in Russian and Polish hard y is a phonemic vowel in its own right.
Since Esperanto is actually by its very birth a slavic-souled language without slavic words, since Esperanto speakers coming from so many languages all tend spontaneously to sound their vowels so as to give the impression of hearing Polish or Serbo-Croatian (though with an Italian-like or Brazilian-like melody) to uninformed ears, since all slavic languages have that sound as intermediate between i and u, it would be stupid and wicked not to acknowledge its presence in Eo, though not phonemic but only aesthetic. The consonant j, when located between two other consonants, should be the natural letter for that closed central vowel sound when an hyphen is not to be understood, as it respresents a consonant consisting in the mere fact of nearing the tongue to the palate, therefore the two cities should be written Brjno and Trjsto.
E is short open e, ee is long open e, and ej is the slightly gliding, English-like long closed e as in grey that can translate any like foreign sound, though technically Esperanto considers it a double sound. Similarly o is short open o, oo long open o, oŭ stands for a long, slightly gliding English o as in glow, low, with ŭ standing for that slight closure of the lips making the o into a closed one (though technically a diphthong by Eo standards). Such a long o sound is not frequent at all in Eo but it is possible nevertheless (though not much liked by present day Esperantists), hence the hesitation between boŭlo and bovlo for English bowl.
But -ŭ and jŭ, that is to say hard i or y followed by a slight closure of the lips, can be used to translate or imitate into Esperanto the French u or German ü sound which quite a number of langauges do have, as the city of Lübeck which Eo should translate as L-ŭbeko or better still Ljŭbeko, or French Namur which should be rendered in Eo as Namjŭro. This can be a nice way to teach Esperantists new sounds of other languages by quite close (and recognizable to the foreign ear) approximations through combinations of pure Eo sounds though not 100% accurate (though most elegant to hear nevertheless).
E is normally open e but it can be nearer a schwa when the law of least effort calls for it, with the result that the diphthong eŭ which is quite present in Eo can be pronounced both with a very distinct open e followed by a closure of the lips, or with a more neutral vowel ending in a closure of the lips more like French eu, as in eŭro (any hurried prononciation of that uncommon diphthong will result rather in the closed schwa French or Dutch like sound, as the closure of the lips indicated by ŭ has to begin as soon as the preceding vowel is uttered. So there you have your long closed schwa. The short schwa is already indicated in common Eo practice by the apostrophe ' and like the hyphen can stand for a silence.
Trump should be normally be written tr'mpo is Esperanto, but since the apostrophe has a semantic value by itself (indicating the blurring or the silencing of an o vowel, among others), it could be also indicated by a mere ŭ standing between two consonants, that is to say a neutral central sound pronounced with a small closure of the lips. Trump should be written Trŭmpo and pronounced quite like the English word with the lips a little more closed as in Northern England rather than in East London where it is closer to a. Without adding new letters nor deforming their meaning that much all exotic vowels can thus be emulated in Eo.