Sanskrit is a very rich language and old language. One word may have multiple meaning.
Language evolve on change time to time. Vedas were at least written around 1500bce.
So how do we know that the translation we are reading and understanding is correct. And that's how people have understood the Vedas when they were first composed.
That is why the Rishis have created four Vedangas: Vyakarana, Nirukta, Shiksha, and Chandas.
- Vyakarana is Vedic grammar and linguistics.
- Nirukta is etymology of Vedic words.
- Shikha is pronunciation of Vedic words.
- Chandas is how Vedic poetic meters are constructed.
Each Vedanga has a set of texts written by celebrated Rishis.
Panini's Ashtadhyayi is a foundational treatise for understanding Vedic grammar. Yaska's Nighantu for understanding Nirukta. The Pratishakhyas for each Vedic shakha are to understand the Shiksha for each Vedic Shakha. Chandas and Pingala sutras to understand Chandas.
On top of this, each Vedanga text was commented upon by several scholars later on. The most notable commentator of Panini's Ashtadhyayi is Patanjali. Patanjali's Bhashya is studied even till today.
In addition to these Vedangas, there is the unbroken chain of Vedic recitation and transmission which is continuing even till today. There are 11 ways to recite the Vedas:
Eleven such ways of reciting the Vedas were designed – Samhita, Pada, Krama, Jata, Maalaa, Sikha, Rekha, Dhwaja, Danda, Rathaa, Ghana, of which Ghana is usually considered the most difficult.
Pada patha is word by word recitation.
On top of this we have the Smritis, which serve as a commentary on the Vedas:
itihasa puranabhyam vedam samupabrahmhayet | bibhetyalpashrutadvedo namayam pratirishyati || - Mahabharata
"One should interpret the Vedas with the Puranas and Itihasas"