TL;DR - The fastest and most efficient way to learn a language is to learn it in a useful way that applies to your daily life. Speaking the language regularly is the most helpful way to increase language learning.

Learning a language is a very difficult thing. Especially when you have either no idea where to start or no one to practice with.
Olly Richards, a polyglot - speaking 8 languages, explains that [speaking a language regularly] (https://www.summerlanguageacademy.com/blog/language-learning), whether you only know a few phrases or words, is the key to learning a language. As with my opinion, integrating a new language into your day-to-day life helps you not just learn a language but utilise it.
I personally am of the opinion that practice makes perfect and when it comes to language learning I think it is the same. Again, another polygot Teddy Nee explains that [you should learn phrases that you actually use frequently] (https://www.summerlanguageacademy.com/blog/language-learning) rather than learning a language form the very basic level.

The highly rated language learning app Babbel also recommends [“keeping it relevant”] (https://www.babbel.com/en/magazine/10-tips-from-an-expert). By this, they mean that if you make it your goal to learn a language for use in conversation, then you are less likely to get lost in textbooks later in you language learning journey. I totally agree with this.

As someone who enjoys language learning, the hardest part, for me at least, it putting all of the knowledge together into coherent and conversational sentences. I believe I have eradicated this problem ever since I started using the language skills I had (very few I must admit) and talking with a penpal as well as a tutor multiple times a week. Language learning is difficult, but to learn it in a more useful and confident way, I believe practicing and using the language is the best way to learn.

TL;DR Some people wake up from comas speaking a different language

Research has found that, on average, it takes an English speaker 480 hours of study and practice to attain basic fluency in an easy language (such as French or Italian) and 720 hours for a more complex one (such a Mandarin or Arabic).

For many, daily practice is the fastest way to learn a new language in order to whittle away at these necessary hours. However, this timescale cannot compare to claims of Foreign Language syndrome, when people become seemingly fluent in a foreign language after suffering a brain injury. These cases are very rare, and often overexaggerated by the media, but in the last 10 years there have been multiple reports and first-hand accounts of this strange phenomenon.

It is theorised that these sudden acquisitions or improvements of a secondary language are due to the sudden loss of the primary language. This is termed bilingual or polygot aphasia, a language impediment caused by brain injuries. Neuroscientists think that fluent speech (primary languages) and non-fluent speech (secondary languages) are stored in different areas of the brain. They suggest that in these cases aphasia prevents the patient from speaking their fluent, primary language, and instead automatically speak in a non-fluent, secondary language that they have some prior knowledge of. Brian Dunning suggests that Foreign Language syndrome patients seem suddenly fluent in their previously non-fluent language because “the brain’s loss of the first language eliminated a slow process that had existed before”; the erasure of the first language also erases the need for internal translation, which can make language learners pause and sound non-fluent. By being forced to rely on a secondary language and without the hindrance of translation, some patients go on to attain true fluency in a matter of weeks even if they regain use of their primary language, making it a fast if unfortunate way of learning a language.

TL;DR: Total immersion is the fastest way to learn a language**

The fastest way to learn a language is complete emersion. This would force you to use a new language every day in relevant contexts. It is possible to use a language every day and not make considerable progress although the desired outcome of using a new language daily will depend on the learner.

[There is evidence that] (https://www.sciencedaily.com/releases/2020/06/200609095027.htm) using a language app daily will improve speaking skills, however solely using this method would deprive other areas of language learning like listening and writing.

TL;DR - Using a language daily embeds the language into the subconscious.

From personal experience, the time when language learning was at its most immersive was when the most progress was made. Take the example of an exchange programme when you are required to speak a different language all the time but also attend lessons being conducted in a different language. This environment, though initially intimidating, forces you to engage with the language at a more intense level than simply language at school. Since you are required to always be using the foreign language, there is not the time to think about what you want to say in your original language and then translate it. You therefore have no option but to learn to think in that language.

In sum, using a language everyday develops essential language skills faster and an intensive environment accelerates the process including those most necessary for becoming fluent in a language, namely thinking in it.

I would say that using a language very regularly is but a single necessary component to learning a language.

It's not that it's the "fastest way" because constantly trying to use a language you know nothing about just isn't enough. You need focused study. But focused study isn't enough to develop comfortable fluency. You need to actually use it.

This doesn't just apply to language. This applies to literally any subject. You can't learn something you can't use and you can't use something you haven't learned.