The word "Anatta" exists in the three marks of existence. In Dhammapada 279, there Buddha says: "Sabbe Dhamma Anatta."
"277. Sabbe saṅkhārā aniccā ti, yadā paññāya passati, atha nibbindatī dukkhe – esa maggo visuddhiyā.
Sabbe saṅkhārā dukkhā ti, yadā paññāya passati, atha nibbindatī dukkhe – esa maggo visuddhiyā.
Sabbe dhammā anattā ti, yadā paññāya passati, atha nibbindatī dukkhe – esa maggo visuddhiyā."
Here first we need to understand the true meaning of word "dhamma".
This word dhamma occurs many time in Pali Canon.
Also, this word "dhamma" is used by Buddha after enlightenment where he meets Ajivika:
"Then, having stayed at Uruvela as long as I liked, I set out to wander by stages to Varanasi. Upaka the Ajivaka saw me on the road between Gaya and the (place of) Awakening, and on seeing me said to me, 'Clear, my friend, are your faculties. Pure your complexion, and bright. On whose account have you gone forth? Who is your teacher? In whose Dhamma do you delight?" -Ariyapariyesana Sutta
"Whose Dhamma" as in "whose path" or "whose truth" or "whose teaching"
So is dhamma "things" as translated by Acharya Buddharakkhita?
"Sabbe Dhamma Anatta" "All things are not-self" - Dhammapada 279
Or is dhamma "phenomenon" as translated by Thanissaro?
"Sabbe Dhamma Anatta" "All phenomena are not-self" - Dhammapada 279
Ajivika: "Whose dhamma you follow?" Or simply whose teaching or path you follow?
Dhamma is dharma. A path. A doing, a way or conduct.
Dhamma is also teaching.
Also, in this book it writes:
"Five hundred monks strove hard but were unable to attain Arahatship, so they approached the Buddha for further teaching; seeing into their past lives and knowing they had previously meditated on lack of self, the Buddha gave them this teaching, after hearing which, they became Arahats.
- Sabbe dhammā anattā ti, yadā paññāya passati, atha nibbindatī dukkhe – esa maggo visuddhiyā.
All components are without self, when one sees this with deep wisdom, then one grows tired of suffering, this is the path to purity." -20: The Chapter about the Path – 245
This could also mean: "See monks all dharma that you have followed is devoid of self. Drop them" or "All paths that you follow is not the self or yourself or that leads to the pure self?
So Sabbe Dhamma Anatta, when one sees this with wisdom, one turns away from suffering. This is the path to purification.
All Dhamma is not-self. All Dhamma does not lead to the path of purity.
All teaching is devoid of essence. All teaching does not lead to the path of purity.
However, in this context, "Dhamma" could really mean existence.
So regarding this Buddha might have said:
"If I — being asked by Vacchagotta the wanderer if there is a self — were to answer that there is a self, would that be in keeping with the arising of knowledge that all phenomena are not-self?" -Buddha (that all dharma, all things, all doings is not the self.)
Now Atta is the core or deep center of something.
Atta is very similar to Atman. But Atta is not Atman. Atman is something only living being consist of. Atta is the core of non-living things as well.
Atta is inside tattva(element). Atta lies even deep.
All "tattva" is made of atta.
Atta is like atom, but concept of atom is new.
You can say Atta is a deep permanent essence that is always there. A core substance.
"Sabbe dhammā anattā ti, yadā paññāya passati, atha nibbindatī dukkhe – esa maggo visuddhiyā.
My translation, in Nepali here: (My native language is Nepali, I have also learned sanskrit as a child. This Pali language is very similar to Nepali and sanskrit.)
'sabbe dhamma anatta ti' : 'tyo sabai dharma ma atta chaina' (there is no permanent essence in all existence.) (here the meaning of dhamma implies all things, all doings, all phenomenon in this world.)
'yada pannaya passati : 'yedi punya paunucha'( if you want to have good merit)
'atha nibbindatī dukkhe : 'ani dukkha nibhauna (and remove suffering)
'– esa maggo visuddhiyā. : 'yo bisuddha marga ho.'( then this is the path to purity.)
So finally it could mean:
"There is no permanent essence in all existence, and if you want to have good merit and remove suffering, this is the path to purity."
What do you think is the correct translation of "Sabbe dhammā anattā."?
It could be true that there was no concept of atman during the time of Buddha, but only "atta" which was later misinterpreted by Hinduism.
Also the word "atta" could also mean "I".