sudanglo:Setting aside whether a sentence like Tiu estas la viro, kiun mi vidis lin (la krimulon) mortigi can be found in the Tekstaro or occurs in speech, there doesn't seem to be any basis for uncertainty in interpretation.

Obviously these sentences are easy to understand, if your first language is English which uses exactly and verbatim this kind of construction.

Miland's idea with "kiel mi vidis" seems to me a lot more understandable, even for non-English speakers.

sudanglo:If you add an object for mortigi (eg mi vidis lin mortigi mian patrinon) there is no uncertainty about who got killed. Again no uncertainty about kiu vidis lin mortigi mian patrinon?, or jen la viro, kiu vidis la krimulon mortigi vian patrinon

Unfortunately both examples are unrelated to the original question, which is about relativizing the direct object of the infinitive. The analogous example would be: Jen mia patrino, kiun la viro vidis la krimulon mortigi. And this sentence is for sure ambiguous.

sudanglo:The structure exemplified by mi vidis lin mortigi is well established and the rule of interpretation is that the part in the accusative (between vidis and mortigi in this case) is considered to be an 'object' of the preceding verb and at the same time a 'subject' of the following infinitive.

"Well established" and a "rule"? So when Zamenhof wrote "[...]Prof-on Michael Foster, kiu esperis nin akcepti en Kembriĝo.", he meant "who hoped for us to accept in Cambridge"? If an object stands between two verbs, there is no rule to which one it belongs. Compare Zamenhof "[...] nur tre malmultaj lasis sin kapti per lertaj vortoj". Here sin is the object of following infinitive and not its subject as your rule says.

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tempodivalse:However, looking at it now, this looks like a bad anglaĵo.

It looks the same to me. Why so complicated, how about:

Mi vidis, ke vespermanĝe ŝi malplenigas du glasojn da vino, kaj tio babilemigis ŝin.
Vespermanĝe mi vidis, ke ŝi malplenigas du glasojn da vino, kaj tio babilemigis ŝin.

(My English isn't good enough to decide which phrase "at dinner" belongs to.)

After all what made her talkative was neither the glasses (La du glasoj [...] igis ŝin babilema) nor the wine, but the act of drinking it.
I think simplicity and ease of understanding should be our paramount parameters when translating.

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miland:Vespermanĝe mi vidis, ke ŝi havis du glasojn da vino. Pro tiuj ŝi nun fariĝis babilema.

This means that at dinner you noticed that she had had two glasses of wine before.

"Well established" and a "rule"? So when Zamenhof wrote "[...]Prof-on Michael Foster, kiu esperis nin akcepti en Kembriĝo.", he meant "who hoped for us to accept in Cambridge"? If an object stands between two verbs, there is no rule to which one it belongs.

Nornen we are discussing vidis iun x-i.

Be a good fellow and have a look in the Tekstaro and see if you can find this structure with vidi (there are plenty of examples) where the bit in the accusative is the object of the following infinitive, or where the bit in the accusative is not the subject of the infinitive.

I haven't thought about whether there is a rule or a pattern which distinguishes the cases where the accusative element is the object of the infinitive (eg mi esperas vin renkonti). Maybe there is, maybe there isn't.

Can you think of a case where 'X-is Y-on Z-i' is genuinely capable of two interpretations - one like esperas vin renkonti and one like vidis ŝin trinki

The thrust of my argument is that starting from mi vidis ŝin trinki having a single interpretation this leads to an interpretation of la vino, kiun mi vidis ŝin trinki.

miland:Vespermanĝe mi vidis, ke ŝi havis (estas ricevinta) du glasojn da vino.

Yes, perhaps havi is not the best verb here. She could have been served two glasses of wine (in error) and not yet have started to drink them.

But vespermanĝe, mi rimarkis, ke ŝi trinkis (estas trinkinta) du glasojn da vino would not necessarily, as Nornen comments, mean that she drank before the dinner. Maybe you noticed her consumption at some time during the dinner.

('mi rimarkis ke ŝi trinkas' would mean noticed that she was drinking)

It's probably worth mentioning that whatever technical ambiguity exists in "kiujn mi vidis ŝin malplenigi", there is little chance of confusion in this specific example because context renders the intended meaning clear enough (glasses do not empty people). So it will be with a lot of phrases of this type.

By the way I did a search in Tekstaro with ki[uo]j?n \w+i \w+\VF (?!kun|nun|en|sen)\w+n \w+i\b and got the following hits:

Tekstaro:
1 trovo en Vortoj de Kamarado E. Lanti
retario de Internacia Junularo Komunista, Franco, kiun mi havis okazon renkonti ĉe la hotelo “Lux”.

1 trovo en Al Torento
en iliaj agoj; eble ili dekomence faris nur tion, kion ili vidis aliajn fari. Eble ilia tuta vivo est

1 trovo en Quo vadis? - Dua parto
te vastiĝis novaj famoj pri ofendoj kaj torturoj, kiujn oni igis ilin suferi en la malliberejoj; kiam

1 trovo en La ŝtona urbo
vis puŝi la balailon sur la planko, imitante tion kion mi vidis lin fari, li kaptis ĝin abrupte el mi

1 trovo en La Ondo de Esperanto
La mondo pli kaj pli komplikiĝas, kaj la demando kiun mi invitas vin konsideri estas: ĉu UEA devas

In every case the object of the infinitive is the relative pronoun, so perhaps this hints at a "rule" of interpretation that could render the meaning clear enough regardless of context.

Looks like I started a real mess here ...

Most of the suggestions offered here are acceptable to express the idea I want to express. However, some seem rather "clunky", like splitting it up into two sentences or other verbose workarounds.

So far, La du glasoj da vino kiujn mi vidis ŝin eltrinki vespermanĝe igis ŝin babilema is the most concise.

My initial problem with that sentence is that it failed the "translation test" - I tried translating it into other languages I know, and figure out if a speaker of that language could comprehend the intended meaning without knowing English.

In Russian, there doesn't seem to be a clean way to express this - you could of course just say Два стакана вина, выпитые ею за обедом, сделали её болтливой (i.e. kiujn ŝi eltrinkis), but where could one insert "mi vidis?"

Question cross-posted to Russian subforum, for anyone who's interested.

EDIT: Now also on the Esperanto-language subforum: http://en.lernu.net/komunikado/forumo/temo.php?t=1... (and Italian http://en.lernu.net/komunikado/forumo/temo.php?t=1..., for maximum outreach).

Given the widely varying opinions in this thread, I thought it would be interesting to seek the opinions of non-anglophones.

I am still not completely certain about this ... as sudanglo says, mi vidis ŝin eltrinki du glasojn should be fine, and yet my intuitions (which are now quite reliable in EO) are not altogether happy with kiujn mi vidis ŝin eltrinki.

I think that the most elegant solution would be to reorder the phrases to remove the broken phrases as much as possible.

This may not be totally correct, but this is what I mean:

Sxi farigxis babilema fare de la du glasoj da vino, kiujn mi vidis sxin eltrinki vespermangxe.

Literally translated, it's not exactly the same (she was made talkative by the two glasses of wine, which I saw her drink at dinner), but I think that it preserves the meaning well.

You might want a different verb in place of "farigxi" ("igigxi" maybe), and I would probably word the second part as "kiujn mi vidis, ke sxi eltrinkas vespermangxe" if that is grammatically correct.

nornen:

miland:Vespermanĝe mi vidis, ke ŝi havis du glasojn da vino. Pro tiuj ŝi nun fariĝis babilema.

This means that at dinner you noticed that she had had two glasses of wine before.

That would be a possible interpretation of the sentence taken in isolation, but in Esperanto the context is often used to resolve ambiguities, and so I don't see it as a big problem. However, if you prefer you could say e.g. Mi vidis, ke ŝi trinkis du glasojn da vino vespermanĝe, pro kiuj ŝi fariĝis babilema

There is a question in my mind, however whether the verb havi is an anglismo in this context. Any views?

Tempo, la demando, kiun vi invitas la forumanojn konsideri estas ĉu tiu strukturo estas tiel malfacile komprenebla, ke ne estos eble al certaj alilingvanoj uzi la anglan kiel interlingvon.

(If foreigners can't cope with 'the wine that I saw her drink', does that mean that English as a lingua franca is doomed?)

Esperanto differs from other languages in that there is no court of final appeal vested in the native speakers to decide whether something is acceptable. The deciding factor is comprehensibility combined with consistency with other elements of the language, moderated with an appeal to economy and elegance.

(And structures in Esperanto do not have to be paralleled in every other language.)

Even in the improbable case that no Esperantist had ever said something like la vino, kiun mi vidis ŝin trinki, or la demando, kiun mi invitas vin konsideri any author might try this out with confidence to see if other Esperantists like it because the meaning of mi vidis ŝin trinki and mi invitas vin konsideri is established.

Tom makes the point about kiujn, mi vidis ŝin malplenigi that 'context renders the intended meaning clear enough (glasses do not empty people). So it will be with a lot of phrases of this type'.

But I do not think we have to rely on that. Simply the function of kiujn and the meaning of mi vidis ŝin malplenigi is enough.

(If foreigners can't cope with 'the wine that I saw her drink', does that mean that English as a lingua franca is doomed?)

English as a lingua franca isn't doomed? What?

A lot of sundry features of English syntax which native speakers take for granted are really not intuitive to (say) a Romance or Slavic speaker. For example, the tendency to drop words or insert new clauses in a non-obvious way - "This needs [to be] done", "I think [that] it's funny", etc.

It doesn't help that English doesn't mark parts of speech well (-ing can be adverbial participle, adjectival participle, gerund, or just part of a root; meanwhile, words like "round" or "light" can be a verb, noun, or adjective without changing forms!). In this way, English is inferior to better-inflected languages in that it causes more problems for comprehension. With a language like French, at least you are in a good position to figure out the parts of speech based on the endings.