Ukrainian border guards and police turned up at the hotel in the city of Lviv where Saakashvili was staying Tuesday and presented him with an official document detailing his alleged violation of crossing the border illegally. However, Saakashvili said in August that he is going to come back to Ukraine from Poland on September 10, 2017.
The Russian Foreign Ministry said in a statement Tuesday that the law is created to "forcefully establish a mono-ethnic language regime in a multi-national state" and alleged that it violates Ukraine's constitution and Kiev's global obligations.
Kiev is "panicking", Saakashvili said, adding that he did "not want to overthrow President Poroshenko" but just defend his rights.
Kiev could leave Saakashvili alone or arrest him and possibly extradite him to Georgia, where the 49-year-old is wanted on criminal charges, which he says are politically motivated.
"We believe that Mikheil Saakashvili can lead our country out of the crisis", Lyudmyla Goretska, one of thousands of supporters waiting in Krakovets on the Ukrainian side of the border, told AFP.
It is "very important not to allow oligarchs to get away with an imitation of reform", Saakashvili said Sunday.
"We need to overcome the oligarchy".
Mr Saakashvili was appointed governor of Odessa in 2015 on the strength of his record of fighting corruption as Georgia's president between 2004 and 2013.
He is now wanted in Georgia on allegations of corruption and abuse of power but claims that the UNHCR recognises him as being "stateless".
Saakashvili divides opinion in Ukraine, which is at war with Russia-backed rebels in its east. He was president at the time of a disastrous five-day war with Russian Federation in 2008, a conflict that his critics argued was the result of his own miscalculations.
Russia on Tuesday strongly condemned a new education law in Ukraine, saying it will infringe on the rights of Russian-speakers.
But he quit in November 2016 amid a dramatic falling out with Poroshenko, who stripped him of his Ukrainian citizenship in July while he was out of the country.
Saakashvili says he does not covet the presidency himself and wants to promote a new, younger politician to the post.
"We see a roll-back of reforms in Ukraine, we see a crackdown on anti-corruption activities in Ukraine".