OK, I feel the need to further explain why <em> can be better than <span> for 1-2 words in a phrase, no matter your point: DIFFERENT LANGUAGE CONTENT inside a phrase, SEMANTIC ISSUES, STYLE HELPERS. And I’d like to make it fun(ny) too. So here it is.
Let’s take this pretend text here. It could be from a site about international dating and mariage.
Don’t jump to any conclusion yet, I’m married seven years now :).
Simple text
[COLOR=“blue”]About international prenup
No matter what motives motif Motive he/she has, you’ve got an offer offre Angebot. Marry marier Einheirat him/her. But a word mot wort is nothing. You also need a document document dokument on paper papier papiere to prevent a wrong conjugation conjugaison konjugation.[/COLOR]
Html fragment for the Simple text
We basically have here a heading and a paragraph, with a few words in different language.
Using default styling (no CSS) and <span> for the foreign words, the html fragment presented by your browser pretty much looks like the simple text.
[COLOR=“Blue”]About international prenup
No matter what motives motif Motive (hey!) he/she has, you’ve got an offer offre(misspeling?) Angebot (is this Ange’s bot). Marry marier(happy, ain’t you?) Einheirat(no need to curse now!) him/her. But a word mot(need a transport, just say it!) wort(worth?) is nothing. You also need a document document(twins are rare, but it looks like you got a pair!) dokument(you fascist!) on paper papier papiere(are you gay?) to prevent a wrong conjugation conjugaison konjugation (is this technical?).[/COLOR]
Reaction: Visual Or reading: Is this a joke? Is it a punk that wrote that? What he’s trying to pull here? And why is it that hard to read? Or hear? This is rubbish!
Using default styling (no CSS) and <em> for the foreign words, the html fragment presented by your browser emphisises, also look pretty much like the simple text, but makes it distinct when a word is in a different language.
Reaction: A little later on. It’s too soon
.
To the Markup
So here’s the basic markup.
<h3>About international prenup</h3>
<p>No matter what motives<span|em lang="fr"> motif </span|/em><span|em lang="de">Motive </span|/em>he/she has, you've got an offer<span|em lang="fr"> offre </span|/em><span lang="de">Angebot</span|/em>. Marry <span|em lang="fr"> marier </span|/em><span|em lang="de">Einheirat </span|/em>him/her. But a word<span|em lang="fr"> mot </span|/em><span|em lang="de">wort </span|/em>is nothing. You also need a document<span|em lang="fr"> document </span|/em><span|em lang="de">dokument </span|/em>on paper<span|em lang="fr"> papier </span|/em><span|em lang="de">papiere </span|/em>to prevent a wrong conjugation<span|em lang="fr"> conjugaison </span|/em><span|em lang="de">konjugation</span|/em>.</p>
We need to sepparate words in a different language. So: <span> or <em>. Both support lang attribute. But they differ in the way of presentation and aureal. Which one is suitable?
Let’s analyze it.
LANGUAGE
Action: <span>, no CSS (just default styling) = no emphasis on foreign words, they look regular (what you’re advocating for). Visually confusing. When reading also confusing: is it a misspeling, an error in transcript?
Reaction: Is this a joke? Is it a punk that wrote that? WWhat he’s trying to pull here? And why is it that hard to read? Or hear? This is rubbish!
Action: <em>, no CSS (just default styling) = distinct emphasis on foregin words. Visually distinct. When reading, also distinct, therefor user (probably,let’s hope so
) understands that it is a translations of the previous word, not a misspeling or an error.
Reaction: Oh, he’s also trying to teach me basic words for a simple conversation with a french or a german. Nice guy this one. Maybe I’ll choose him. 
SEMANTIC
Not much to say here. <span> can be used. But it means nothing. So it has no purpose. <em> is a proper semantic choice. It’s a phrase element, so it’s in the right place. Serving the obvious role of separating obviously different (another language) content. And that needs to be emphasised. A good practice. Let’s do the math.
Semantic(phrase) + Semantic(em) = Semantic(phrase)
Semantic(phrase) + BlankSemantic(span) = SnowWhiteSemantic(phrase) ?
STYLE
<span> has no style (you can say that again!). <em> has just a little style (oh, that’s not nice of you to say!).
Both can be easilly blue, or green, or brown, depending on the language, if you want. Or have a different font style, repressentative to that country. Or decorated in some way (say a little flag preceding the word). Without the need to resort to any hacks. And the lang attribute works great for both as an attribute selector. My word: Don’t let the style stand in your way! 'Cause it’s not.
The Markup Revisited
I present you a clever mark-up, a mark-up as I see it, that makes the right use for <span>, as a container for inline elements.
<h3>About international prenup</h3>
<p>No matter what motives<span class="foreign"><em lang="fr"> motif </em><em lang="de">Motive </em></span>he/she has, you've got an offer<span class="foreign"><em lang="fr"> offre </em><em lang="de">Angebot</em></span>. Marry<span class="foreign"><em lang="fr"> marier </em><em lang="de">Einheirat </em></span> him/her. But a word<span class="foreign"><em lang="fr"> mot </em><em lang="de">wort </em></span> is nothing. You also need a document<span class="foreign"><em lang="fr"> document </em><em lang="de">dokument </em></span>on paper<span class="foreign"><em lang="fr"> papier </em><em lang="de">papiere </em></span>to prevent a wrong conjugation <span class="foreign"><em lang="fr">conjugaison </em><em lang="de">konjugation</em></span>.</p>
So here it is. I’ve challenged my self to make an example that proves my point.Try both examples in a browser and see the difference.
Awating proposals 