All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
There is no doubt that talking about religion in general and about Allaah's Attributes and Beautiful Names in particular, should be with knowledge, and talking without knowledge is very serious, as the questioner remarked. Allaah says (which means): {Say, "My Lord has only forbidden immoralities, what is apparent of them and what is concealed, and sin, and oppression without right, and that you associate with Allaah that for which He has not sent down authority, and that you say about Allaah that which you do not know."}[Quran 7:33]. Allaah further says (which means): {And do not pursue that of which you have no knowledge. Indeed, the hearing, the sight and the heart about all those [one] will be questioned.}[Quran 17:35].
Allaah further warned us against practising deviation about His Names, as Allaah says (which means): {And leave [the company of] those who practice deviation concerning His names. They will be recompensed for what they have been doing.}[Quran 7:180].
To conclude, speaking about the Religion of Allaah should be with knowledge and not out of ignorance and according to one's desires. However, saying that Allaah is the Truth and that He is Beautiful is not considered as lying about Allaah or speaking about Him without knowledge as this is something upon which there is evidence in the Book of Allaah and the Sunnah of the Prophet . Allaah says (which means): {That is because Allaah is the Truth, and that what they call upon other than Him is falsehood, and because Allaah is the Most High, the Grand.}[Quran 31:30].
In addition to this the prophet said: "Allaah is Jameel (which implies beauty) and He likes beauty." [Muslim]
Therefore, one should know that the bounds of informing about Allaah are wider that His Names and Attributes, i.e. that we cannot name Allaah with a name or an attribute except with what Allaah has named Himself in His Book or that the Prophet named Him with. However, informing about Allaah does not necessarily have to be using something that is mentioned in His Book or in the Sunnah of the Prophet . For example, one could inform (people) that Allaah exists and that He is known when he debates with the people who deny that Allaah exists, but one should not say that existing and being known are amongst the names or attributes of Allaah, so there is a difference between informing and naming.
Allaah knows best.