Let's say that Otuin the High Elf and Barlak the Dwarf want to meet and trade languages.  They get together in the same zone, preferably a very safe place such as a city, and group. They go to a zone boundary and, without crossing it, sit down facing each other next to the zone line.

Now, Otuin must set up a "spam" macro.  He does this by picking one of the buttons on the Socials menu and right clicking on it.  That brings up a new window with a name (which Otuin can change to "spam" or whatever name he prefers) and five lines.  Otuin should fill up all 5 of those lines with /groupsay statements such as:

/g I have walked out in rain and back in rain.
/g I have outwalked the furthest city light.
/g I have looked down the saddest city lane.
/g I have passed by the watchman on his beat
/g And dropped my eyes, unwilling to explain.

(a fragment of a poem by Robert Frost)

Then Otuin should drag this new Social button over to his hotkey box and drop it in an available slot.  Otuin now has a hotkey which will groupsay those five lines whenever he activates it.

Next, while he is in windowed mode, Otuin right-clicks on the chat window.  This brings up a new window which includes such information as which language Otuin is speaking.  Otuin left-clicks on the language until it cycles to "Elvish."  He then right-clicks on it to dismiss that new window.

Meanwhile, Barlak has been doing the exact same thing, except that he has selected "Dwarvish" as the language he will speak.

Now the lesson begins.  Barlak and Otuin begin to user their hotkeys (either clicking with the mouse or pressing the right numeric key, whichever you find more convenient) to "spam" each other with their respective language.  Barlak yammers at Otuin in Dwarvish, and Otuin chatters right back at Barlak in Elvish.  While this is happening, lines of gibberish are filling up their chat windows so fast that there is no possibility of successfully using the /say or /tell commands, or hearing anything shouted or told or said to them.  This is why they need to be in a safe place (like a city); they cannot hear any warnings anyone tries to tell them, and moreover, if a monster does run up and start hitting them, they will not even notice until they see the change on their health bar.

There is a way around this, however.  Simply go to the "chat filters" submenu of the "options" menu, and turn group chat off.  The you will not see the other person's spam, though your skill in that language will still improve.

While the lesson is underway, each should see the message "Your language skills have improved!" appear in their chat window from time to time.  It is necessary to watch closely, as it scrolls off very quickly.  Eventually Barlak or Otuin will stop seeing that message.  When that happens, he should stand up.  Standing up is the signal that the language lesson needs to stop at least temporarily.  Now both of them should cross the zone line.  Zoning is necessary because otherwise you will not be able to judge your progress.

Once both of them are in the new zone, Barlak and Otuin should check their skill list to see how good they are at their new languages.  If Barlak's Elvish is now "Excellent" and Otuin's Dwarvish is also now "Excellent," then the language trade has been a complete success.  If that is not the case, then they need to sit down and repeat the process until they both speak the other's language Excellently.
 

Aspen Alemaker, monk of the 26th rank (Mithaniel Marr server)
Sister of the Ashen Order, orange kyu
Member of the Silent Fist, red kyu
master linguist
master brewer
master cook
apprentice smith
apprentice tailor
Mayor of Qeynos