"I just had a wonderful trip."

Translation: Mi ĵus havis mirindan vojaĝon.

[ptrck_hrmn]

Why does the Esperanto word "ĵus," being an adverb, not end in the letter <e>?

[mizinamo]

Because not all adverbs end in the letter e.

There are some roots that can be adverbs, adjectives, nouns, or verbs depending on the final letter, but some words that can only be adverbs and that are not composed of roots plus the ending -e.

Ĵus is one of them; others include nun, eĉ and a number of words that end in the quasi-ending -aŭ such as hieraŭ, hodiaŭ, baldaŭ, almenaŭ, kvazaŭ.

That said, you can turn many of those into other parts of speech (particularly adjectives) by treating them as roots and adding an appropriate part-of-speech ending: nuna "current", ĵusa "immediately preceding", hieraŭa "today's".

But nune, ĵuse, hieraŭe etc. are not usually used; they're sort of doubly-marked for adverbness.

[ptrck_hrmn]

Dankon!

[psifish]

I completed the affixes 1 lesson, so I thought I would try using my new found knowledge here by using the "eg" affix with "bonan". I answered "Mi ĵus havis bonegan vojaĝon" and Duo accepted it. I am now wondering if "mirindan" and "bonegan" have different connotations, or if they are interchangeable.

[mizinamo]

Well, bonega = bon'eg'a = very good, and mirinda = mir'ind'a = worthy of being marvelled at, wondered about.

So "mirinda" is more strictly "marvelous, wonderful" and "bonega" is literally "very good". They're both positive but not exactly the same.

[filopodia_]

Why can I not always switch the order of the noun and the adjective? Sometimes Duolingo accepts my answer regardless of the order of the nouns and adjectives, but in this case, placing wonderful after the word trip is rejected. I thought that it could be done either way in Esperanto (noun then adjective or adjective and then noun) and adjective after the noun just makes more sense to me :(

[ptrck_hrmn]

From what I understand, it shouldn't matter. In one of the earliest lessons (accusative, I believe), it was made extremely clear that word order is very free in Esperanto. I think your problem might actually be a problem with Duo's translation, not yours. Try reporting it and see?

[filopodia_]

Dankon!
That's what I thought was made pretty clear at that point too, but it seems the further I get into the lesson 'tree' the less it accepts the order of noun-adjective. Earlier lessons that ordering was perfectly fine. Very strange.

[mizinamo]

Because they further you get in the tree, the fewer pioneers have gone before you and reported "missing" alternatives :)

The team can't think of every possible permutation in advance (because Esperanto is simply too flexible) and so they rely partly on people reporting sentences they hadn't thought of before.

So the existing alternatives will be the more common ones (e.g. subject - verb - object; adjective - noun) and different word orders will probably only be added once someone reports the alternative on a given sentence.

Your Duo experience might be better if you stuck to more "boring", English-like alternatives rather than showing how clever you are by exploring Esperanto's possibilities and having to keep reporting sentences the team hadn't thought of before.

[filopodia_]

Hmm that makes a lot of sense, thank you!
It's just a little frustrating because I also speak Spanish and the noun-adjective order sometimes seems more 'natural' to me depending on the sentence than the traditional English order does (though in this case the noun would be adjective then noun anyway; this sentence was just the one that made me question the adjective placement rules of Esperanto). And, because of that, the freedom of word order that Esperanto allows is really nice, though, as you point out, that freedom does make the team's lives much harder!

[ptrck_hrmn]

That is odd. I've been trying to keep a basic English-esque word order as I translate, but I've thought of this as personal preference. Hopefully Duo the all powerful Strigo will fix this issue soon.