I've had my eye on Esperanto in the same way I've had my eye on Klingon and Elvish. There's something about a constructed language that fascinates my inner geek. But I don't have any experiences to share.
I look at it this way:
Learning Esperanto probably won't make learning Japanese harder for you except by taking away time that could be spent on the latter language.
Therefore, the balance is between time spent learning Esperanto versus time saved learning Japanese. This is ignoring any other benefits of learning Esperanto.
The numbers I saw earlier in this thread -- 200 class hours to learn Esperanto and 2200 class hours to learn Japanese -- seem like a reasonable ratio to me. You can adjust the numbers as you like. If we go with this assumption, then the break-even point is when Esperanto reduces that load to 2000 class hours, or 91%.
That is, you get Esperanto for free if it can increase your Japanese-learning proficiency by 9%. And it's a good deal even if it doesn't.
If Esperanto increases your efficiency by more than 9%, it's like getting two-for-one for less than the cost of Japanese alone, i.e. learning Esperanto should be a part of every Japanese-language curriculum in that case.
We know it is possible for that kind of relationship to exist because learning Heisig does the same thing for holding the Kanji shapes and basic meanings in your head.
That's begging the question, but I think we all agree on this point or we wouldn't be here.
A better example is addition. If we can understand a single, fundamental rule for adding, it saves us an infinite lifetime of blind memorization.
Interestingly, it seems this is not a commutative relationship. Order matters. For example, if you learn all the kanji without Heisig, it doesn't help you to go back and learn Heisig. You must learn Heisig first to get the benefit.
To rephrase the original question: Can Language A provide some fundamental understanding that boosts the learning of Language B significantly?
It's hard to answer that question because it's not falsifiable. I can't say that it won't. I have no evidence that it is. I can only say how likely I think it is, which doesn't help much, because unlikely things happen every day.
So I'll try to identify some ways in which it
could help.
One way is overlap. If they share some grammar, sentence order, words, etc. learning one is the same as learning parts of the other. In the best case, both languages are highly similar, like English and
Lowland Scots.
This is a purely linear relationship.
That means, in the best case, if you spend 200 class hours learning Language A, you save at best 200 class hours on language B. For example, learning
Simple English will save you almost as many hours learning native English as is put into it, but no more, because it is a subset of English.
This relationship is probably commutative. But I'm looking for something more fundamental; something that upsets the balance.
Such a relationship might lie within the way the mind works.
Language learning starts with acquiring a large library of words, sentences, grammar points, etc. This is a linear process, as described above. But gathering and holding these new facts in addition to existing, conflicting facts from the primary language is something new.
Language fluency requires being able to apply your new knowledge on the fly. This means thinking in different patterns.
These are new ways of using your brain that you do not know when you spoke a single language.
If this is correct, then we have established our imbalanced relationship. Learning Language A (easy)
to fluency may very well provide a significant, non-linear benefit when learning Language B (hard). Learning Language B (hard) first would provide a similar benefit when Language A (easy), but the gains would be unequal. For example, in the first case you might save 200 class hours, but only 20 in the second.
Based on the many assumptions I've made, and recognizing the inexhaustiveness of this approach, I come to the following tentative conclusion:
You'll probably benefit from learning any second language to fluency, and the easier and quicker the better. Esperanto's a good candidate because of its simplicity and uniformity.
But I cannot conclude how much of a benefit there is. Only that it is reasonable that there might be one.
Finally, I put forth a new hypothesis*: The sentence method of
AJATT may be even more efficient.
Since it collapses the mental process into one step, at every point along the way you are fluent with the knowledge you have acquired. That's probably why he stresses that you need to understand each sentence, not just memorize it.
-- Daniel
* Not to be confused with an actual hypothesis.