After the conversation yesterday about grammar putting someone off learning another language, I thought I would put together a few thoughts about what the easiest language to learn is.
This is really two questions. One of them concerns all language, and is basically this: which language would it take a baby the shortest time to learn? The other is more about adults who are already fluent in at least one language: which language is quickest to learn for someone who already speaks, say, English?
The first question is not as straightforward as it sounds. A foetus which can hear is exposed to spoken language before birth and it has been shown that new born babies adopted into different linguistic communities than their parents do in fact learn to speak more slowly than those adopted by parents who speak the same language. So far as I know, there is no difference in how long it takes for babies to learn to speak any particular spoken language, although it is sometimes claimed that children are more likely to have a speech impediment in certain languages, for instance Czech, whose children are allegedly more likely to mispronounce the sound "ř", which is generally supposedly the last sound they learn to say. This probably means the sound is going to die out soon because in a way it's small children who create the language - they will be the ones who grow up to "break" grammatical rules and pronounce things differently, thereby changing the language for everyone. There are also a few languages whose sounds are easier for the speakers to pronounce because of physical differences in their mouths and throats. The click languages of Southern Africa are clearer when pronounced by the San themselves because their palettes are higher, giving them more resonance. Conversely, Japanese people are likely to find Arabic and other related languages harder to pronounce than their native speakers because they often lack the musculature to close their throats enough to say the emphatic consonants found in those languages. Therefore, whereas these are not the easiest languages, it is literally harder for the non-San to learn click languages and for Japanese people to learn Arabic.
The second question is of course highly relative, and it also depends on what counts as a foreign language. Nowadays, there is more recognition of separate languages than there used to be and it was once said that "a language is a dialect with an army and a navy". If the People's Republic of Yorkshire really existed, maybe the language of Yorkshire would be considered a separate language to English, for instance, and of course Scots nowadays is, although its lack of a standard complicates matters somewhat. It might be thought that the languages closest to English are the easiest for an English speaker to learn. These would be the other Ingvaeonic languages, and at this point I will furnish you with a map:
It might be thought that for an English speaker, these will be the easiest languages to learn as they are its closest relatives. However, this language has an unhelpful history here because of the Vikings and Normans coming over here and taking over the language by introducing their own words. Nonetheless, look at this:
Fade teil thee zo lournagh, co Joane, zo knaggee?
Th' weithest all curcagh, wafur, an cornee.
Lidge w'ouse an a milagh, tis gaay an louthee:
Huck nigher; y'art scuddeen; fartoo zo hachee?
This is Yola, translated into English thus:
What ails you so melancholy, quoth John, so cross?
You seem all snappish, uneasy, and fretful.
Lie with us on the clover, 'tis fair and sheltered:
Come nearer; you're rubbing your back; why so ill tempered?
It doesn't really seem to be English, does it? It's a bit Englishy, to be sure, but it's not the kind of thing you wouldn't need to learn.
Similarly with West Frisian:
Us Heit, dy't yn de himelen is
jins namme wurde hillige.
Jins keninkryk komme.
Jins wollen barre,
allyk yn 'e himel
sa ek op ierde.
Jou ús hjoed ús deistich brea.
En ferjou ús ús skulden,
allyk ek wy ferjouwe ús skuldners.
En lied ús net yn fersiking,
mar ferlos ús fan 'e kweade.
Want Jowes is it keninkryk en de krêft
en de hearlikheid oant yn ivichheid.
That's the Lord's Prayer.
I've found North Frisian easier to follow than West Frisian for some reason I don't understand, but this may be due to my knowledge of German. West Frisian really isn't easy to understand at all because all sorts of weird stuff has happened to it since the Dark Ages, mainly at the hands of the Dutch.
More promising is Tok Pisin, a language spoken in Papua. Here's the Lord's Prayer in that:
Papa bilong mipela, yu stap long heven. Mekim nem bilong yu i kamap bikpela. Mekim kingdom bilong yu i kam. Strongim mipela long bihainim laik bilong yu long graun, olsem ol i bihainim long heven. Givem mipela kaikai inap long tude. Pogivim rong bilong mipela olsem mipela i pogivim ol arapela i mekim rong long mipela. Sambai long mipela long taim bilong traim. Na rausim olgeta samting nogut long mipela.
This is not too hard, but it's easier to understand than speak.
So much for closely related languages then. They don't seem to be at all easy to learn.
The Romance languages are a somewhat better bet. French shares a lot of vocabulary with English although its pronunciation is very different and hard for English speakers. Take that away and you have Castilian Spanish and Italian, which are easier to pronounce and still have words which are quite familiar although the grammar is more inflected than French.
A language vaguely based on Romance and actually designed to be easy to learn is Esperanto. Research shows that speakers of Western European languages generally learn it about four times faster than the average foreign language. It has a very small vocabulary modified by large numbers of prefixes and suffixes, and has fairly minimal grammar Even so, it isn't actually that easy because Ludwik Zamenhof, who invented it, was Polish and like many other people tended not to notice the bits of his language which other people found peculiar and difficult, which is probably why it has six verbal participles rather than the more usual two found in most widely spoken European languages such as English ("taking" and "taken" for example) along with consonants stuffed together which would often be seen as hard to pronounce and perhaps even not well-defined as to rules such as "kv" in words like "kvankam", which could be either "kfankam" or "gvankam" depending on your first language. Then there are things like "lernejo" meaning "school" when most other widely spoken languages use a word like "school" and the word "neutrino" meaning "female eunuch" rather than referring to a subatomic particle, due to the way words are put together. Nonetheless, it is in fact fairly easy to learn.
Abandoning Europe, things can be easier. There are certain languages whose grammar is so easy compared to English that you wonder why we even bother. Mandarin Chinese, for example, doesn't even bother with plurals on the whole, except for pronouns. It is, however, complicated for an English speaker by having tones, so it's possible that the sentence "Ma ma ma ma ma" can mean "get the horse, a mad dog is coming" or something completely different, and that does a lot of people's heads in unless they already speak a tonal language. However, Mandarin Chinese has fewer than two thousand words, each of which has only one syllable, and is incapable of constructing any more, so that makes learning the vocabulary easier, although it does sometimes cheat by using "words" which only make sense next to each other such as the word for "insect", which then effectively becomes a two-syllable word.
If you prefer an easy language without tones, you could do a lot worse than look at the Austronesian tongues such as Malagasy, Samoan, Maori and Malay/Indonesian. This family has in fact been geographically the most widely spoken in the world, but many of its languages only have a few speakers because many of them live on small, remote islands in the Pacific and Indian Oceans. On the other hand, Malay/Indonesian is spoken by 220 million people, and it's this language which I always think of as the easiest language in the world, for almost anyone, not just English speakers. No plurals, or plurals expressed by saying the word twice, the verbs don't change, no gender, uses the noun referred to instead of "it" and so forth. It's not even hard to spell or pronounce, it has no sounds hard for English speakers to say, doesn't put them together in a way we would find hard either and in general, it's ridiculously easy. It raises the question of why other languages even have all that stuff if they don't need it.
So for English speakers, the answers to the question are probably these:
Tok Pisin is the easiest language to understand and West Frisian the second easiest.
Spanish and Italian are the easiest languages to learn and pronounce clearly.
Esperanto is pretty easy to understand and speak apart from the verbs being weird and you can learn it quickly although you won't find anyone to use it with.
Malay/Indonesian is the easiest to learn in terms of grammar, spelling and pronunciation but most of the vocabulary is very unfamiliar and you would have to learn a lot of words.
Mandarin Chinese has simple grammar and a tiny vocabulary, but is written in a way which is hard to learn and has a lot of words which mean lots of different things, and the tones also make it hard.
So I'm going to say Malay/Indonesian.