Is important to understand that Hindi is an Indian language.
All languages of Indian origin tend to be rather tough for foreigners to master. In fact, these languages can be rather tough for other Indians to master as most of these languages differ quite a lot from each other. Although these languages are rooted in the same ancient godly language of Sanskrit, there are too many differences among these languages which makes it rather difficult for speakers of different languages to master other Indian languages.

With that said, Hindi is one of the most popular languages in India and is the most commonly associated language with the country of India.
40% of the Indian population speaks Hindi. And many others learn it as their second language. Therefore, Hindi is pretty popular in India.
Keeping this in mind, if you want to learn Hindi, then re-learning it will never be a problem.
The reality is languages like Hindi, Chinese, Japanese, Korean, etc are considered to be one of the toughest languages to master. This also means that if you mastered it, you can never truly forget the entire language.
So the question still remains, how do you relearn Hindi?
There is a pretty simple answer to this question. This answer is basically a ratio. You want to read in any language, you need to divide the language into three parts and then evaluate on the basis of a formulated ratio.
First, start off with nothing down all the things that you perfectly remember in Hindi.
These are basically those things that required no real learning or even revision for that matter. You know and remember these things by heart.

Next stop, note down all of those things that you remember vaguely.
These are things that you remember to some extent but most definitely requires some revision for clarity.
Finally, note down all of those things that you seem to have completely forgotten or things that have completely slipped out of your memory at least for the time being and make a ratio.
With all these three separate factors, note it down, you can create a simple ratio. This ratio will denote how much you remember in regards to the language and how much you don’t.
Finally, you can analyse this ratio in order to realise how long it would take for you to relearn the language.
If you remember more than what you have forgotten, then you will not take as long to relearn the language. On the other hand, if you seem to have forgotten more than you seem to remember, then you will most definitely take a long time to re-learn the language.
You can also decide different ways of reading a language on the basis of this ratio.
For example, if you remember more than you have forgotten, then you can simply opt for self-learning.
