Hanaseru

Now, "best" is a very subjective term.

In what manner are you talking about?  The most useful languages? The most fun languages?

As for the most useful languages, it is still a very subjective way to group things.  What makes a language more useful than other?  The number of native speakers?  The number of people who learn said languages?

Native Speaker quantity-wise, Chinese and Arabic would come out on top, but Chinese and Arabic are rarely spoken outside of their geographical areas and thus may lose the value of having more native speakers.

Learner quantity-wise, English and Spanish would (probably, I didn't really fact check for this) come up on top.  While I definitely agree with English being a very useful language, I'm a bit doubtful about Spanish.  Studies have shown that Spanish is not so valued in the workplace (people who are bilingual in spanish and english only have a 1% higher income than english-only speakers), so its value seems to be exaggerated.

Personally, I vouch for learning uncommon languages, as those languages are much less commonly studied and can really open your eyes to a different point of view.

I do not believe that Chinese will become a globalized language.

China, although it has the economic capabilities, does not have enough social nor cultural influence in Western society.  English became globalized because the US and GB together were able to exert a huge amount of influence throughout many countries, even in Asia. 

I can see it happening in Asia though (which it has already happened in, as classical chinese was the lingua franca of the Far East), as many Asian societies have been heavily influenced by Western traditions.

At one point, I wanted to learn Korean.

Unfortunately, I gave up because the orthography did not correspond very well with the phonology (g's being pronounced like k's, random ngs appearing, etc)

I think that Rosetta Stone can be quite useful (but not for every purpose)

The best thing I've ever gained from Rosetta Stone is smoother communication.  There are a lot of speaking drills, and they really help out with learning how to speak properly.

I think it's perfectly possible to learn an accent.

Every accent has its own patterns, and so you can learn the accent by analyzing speakers of the accent's phonological patterns and apply them to your own accent.

For example, I live in Staten Island (or as we call it here, Sta'n Eyelan).  We often pronounce words that have the ah sound with an åh (kind of like aow) sound, such as in Sausage.  This rule can be applied to other words, with that sound, such as Coffee.

I like songs in other languages mostly for the sound of the melody.  Eventually, I'll pick up a few words here and there (especially if I'm learning the language that the song is sung in)

社会　（society)

この社会は世界の第一です。

I probably can read 2-3k of them ((in chinese)), but in Japanese, I've only learned about 300-400.

Many of the onyomi readings can be "derived" from the chinese readings though, and oftentimes, so can the meanings.

Also, I've always heard that the Joyo kanji isn't enough, and that you really need about 1000 more to be able to understand newspapers, books, etc fluidly.

I don't use lol per se, but I tend to use lel more and more often recently (i'm not one of those people who start and end sentences with it though)

It would probably be best if there was a way to have a "neutral" language so that it didn't imply and sort of superiority of one language over another.  It also would keep politics out of the mix.  I am not a trekkie, but I would rather see Klingon than any real language.  With technology today, I am sure someone could write a program which could merge all languages into a sort of blend.  How diplomatic would that be?

If you were to blend languages together, then how would you determine which aspects of a language go into the main language, and which aspects don't?  Same with vocabulary.

Conlangs never really took off.  It's really hard to promote a language that nobody knows yet.

English became the global language because of the influence of the Anglosphere, but conlangs do not have the backing of a certain influence huge enough to be made into a lingua franca.

I think that owning a dictionary is still useful just for the page flipping experience.  While searching for your word, you might stumble upon other words that you might just absorb into your memory.

Depends on how "uncommon" the languages are. 

The most uncommon language I personally want to learn is Finnish, but I also want to learn Swedish, which does not have a lot of speakers either.

I think that all 3 are around the same difficulty, with maybe reading being a bit easier than the others.

Writing: You really have to recall vocabulary and you have to be able to put them into coherent sentences

Reading: You have to make sense of a group of words, although you can probably guess for part of it with context clues

Speaking: You have to think of words quickly enough.  Grammar is much more forgiving in the spoken language.

若い　（young)

僕たちは若いでございます。

When I have children, I'll make try to make them at least trilingual from birth.

People always said that it's easiest to pick up a language as a baby, so might as well get some then.

見る　（みる see)

あなたに海を見せる。

Requiring correct grammar is such a prescriptivist stance, but when learning a new language, I think it can be necessarily to learn the "correct grammar".

(Slang to me has its own "correct grammar" too )

I have to translate French and Spanish every once in a while

Finnish ^^

The pronunciation is easy and everything.

I've never really found Rosetta stone that helpful, but that may be because I stopped after the first section.

Personally, I like the Pimsleur method much better.

I have mostly a general american accent, but I've picked up a few bits and pieces of the Staten Island accent (new york city / jersey accent)

En école, je viens de regarder deux films français (Jean de Florette et Manon des Sources).  Ils étaient très tristes, mais je les aime.

難しい　（difficult)

日本語はとても難しいでございます。

Well, I partly agree. However, I do not think that English will be dominant because it sounds especially nice or beautiful, but simply because English is easier to learn than Chinese. However, this only holds true for some aspects. Chinese Grammar, for instance, is really easy and compared to English Grammar I would even go so far to say that Chinese Grammar is (much) easier than the Grammar of the English language.

Continuing on that statement, I'll argue that English is one of the hardest languages in the world, especially in pronunciation.

Studies have shown that native speakers of English took 2 extra years to reach the same fluency in reading as those of other European languages.

Pronunciation in English is full of rules with many exceptions.  This makes it very hard to discern the pronunciation of a single word without having heard it before.  Seems just like Chinese characters.  There is also a stress accent in English, just like the tones in Chinese, for when you change the stress on words in English, sentences can have drastically different meanings.

Swedish verbs are categorized into several groups and sub-groups. I would say that there is no one basic rule for present and past tense of verbs, and you have to know each of them by heart if you are to use them properly. One example, which is the easiest, is the first verb group. These are words that end with the letter a in its infinitive form. The word "show", meaning to "show someone or something" translates directly to the verb "visa". It then becomes

Present tense: visar  = showing

Past tense: visade = showed

Supine or Past Participle: har visat = has shown

Other verb groups transform according to what letter they end, or how the last letter or vowel of the verb sounds. To answer your last question, irregular verbs are the most difficult to learn because they have separate rules, where the vowels change when the verb is used in present, past, and supine tenses.

Pardon me if I get this wrong (my swedish isn't SOOO good)

About irregular verbs,  many of the irregular verbs in Swedish are also irregular in English (strong verbs)