Here are links to three relevant relevant articles, with excerpts.

Outline of the Tiantai Fourfold Teachings 天台四教儀
Compiled by the Goryeo Śramaṇa Chegwan 高麗沙門諦觀, Translated by A. Charles Muller

一未度者令度。卽衆生無邊誓願度。此緣苦諦境。
All those who have not yet been saved will be saved, which is expressed as “I vow to save all living beings without limit.” This vow takes the truth of suffering as its referent.
二未解者令解。卽煩惱無盡誓願斷。此緣集諦境。
All those who have not yet understood will be made to understand, which is expressed as “I vow to extinguish all afflictions, no matter how exhaustive they may be.” This vow takes the truth of arising as its referent.
三未安者令安。卽法門無量誓願學。此緣道諦境。
All those who have not yet been comforted will be comforted, which is expressed as “I vow to study the teachings, however numerous they may be.” This vow takes the truth of the path as its referent.
四未得涅槃者令得涅槃。卽佛道無上誓願成。此緣滅諦境。
All those who have not yet attained nirvāṇa will be enabled to attain it, which is expressed as “I vow to attain supreme enlightenment.” In this vow they take the truth of cessation as their referent.

An Introduction to Tendai Buddhism by Seishin Clark

In the Tendai School of Buddhism we take the Four Bodhisattva Precepts 四弘誓願 (Shigu seigan – Four Great Vows):

Sentient beings are numberless; I vow to save them all.
Afflictions are inexhaustible; I vow to end them all.
Schools and traditions are manifold; I vow to study them all.
The Buddha way is supreme; I vow to complete it.

These are said to have been composed by Venerable Zhiyi (Zhiyi) who was the founder of Chinese Tendai (Tiantai). They embody the Bodhisattva path (enlightenment for all beings), as well as embodying the Four Limitless Virtues (四無量心 Shi muryō shin):

1. Maitrī – Loving kindness. The act of good will to all others
2. Karuṇā – Compassion. The act of identifying oneself with the suffering of others
3. Muditā – Joy. More specifically, taking joy in the joy of others. Also known as empathetic joy.
4. Upekṣā – Equanimity. The treating of everything and everyone impartially with complete serenity.

The Four Extensive Vows and Four Noble Truths in T’ien-t’ai Buddhism
Robert F. Rhodes (1983)

Chih-i here gives two versions of the Four Extensive Vows:
1. Those who have not been ferried over, (I will) ferry over.
Those who have not yet understood, (I will) cause them to understand.
Those who have not settled themselves, (I will) cause them to be settled.
Those who have not attained (nirvana), (I will) cause them to attain nirvana.

2. Sentient beings, limitless in number, I vow to ferry over.
Passions (klesa) which are numberless, I vow to extinguish.
The Dharma-gates without end (in number), I vow to know.
The supreme Buddha Way, I vow to actualize.

The first set of vows is taken from the Lotus Sutra (T9, p. 19b), while the second is original to Chih-i. This enumeration of vows is followed by the statement that each of these vows correspond to one of the Four Noble Truths.

The Lotus Sutra quotation is from Chapter Five, “Medicinal Herbs”.
In Burton Watson’s translation:

Those who have not yet crossed over I will cause to cross over,
those not yet freed I will free,
those not yet at rest I will put at rest,
those not yet in nirvana I will cause to attain nirvana.

In Bubo and Yuyama

I set free those who have not been freed.
I enlighten those who have not been enlightened
and bring calm to those who have not been calmed.
I cause those to obtain nirvana who have not yet obtained it.

In Cleary:

To those who are not yet saved, I bring salvation.
To those who are not yet liberated, I bring liberation.
To those who are not yet at peace, I bring peace.
Those who have not yet attained nirvana, I enable to attain nirvana.

Here’s the original (Kumarajiva’s Chinese):
未度者令度，
未解者令解，
未安者令安，
未涅槃者令得涅槃

The title of the Chapter in Chinese is 藥草喻, literally: medicine grass metaphor.
http://tripitaka.cbeta.org/T09n0262_003

Let’s take a look at some of the Chinese characters:
未 means “not yet” and “令” means “now”.
者 is a particle that can be used to mean “those who”, referring to what came before, like in the following Chinese saying:
知人者智，自知者明
Literally: know other those-who clever, oneself know those-who wise
So each of the four follows a set pattern:
Not-yet X those-who, now X.
Where X =
1. 度 save, saved, salvation, ferry-over
2. 解 mokṣa, liberation, freedom
3. 安 peace, stillness, serenity, tranquility
4. 涅槃 nirvana

Note that in #4 there is an added character: 得, attain or obtain. One might conclude that this is implied in the first three, but made explicit in the last one for emphasis.

According to the Digital Dictionary of Buddhism, 解 can also mean “understanding”, “knowledge”, “dissolving doubt”, “to make clear”, or “to explain”. If we accept this translation of 解 then we have, roughly:

1. Those not yet saved, I will save,
2. Those who do not yet understand, I will teach,
3. Those not yet at ease, I will put at ease,
4. Those not yet in nirvana, will cause to attain nirvana.

If we swap 2 & 3, the above can now be transmorgrified into the Four Great Vows if we
1. Explicilty make “sentient beings” (衆生) the referent of “those who”.
2. Equate “cutting off” (斷) the “kleshas” (煩惱) with “being at ease” (安).
3. Equate “learning” (學) the “Dharma gates” (法門) with “understanding” (解).
4. Equate “accomplishing” (成) the “Buddha way” (佛道) with “attaining nirvava” (得涅槃).