aswaha and katawaha in Buddhism

If this interpretation of those words of those words is correct, then FYI I think that is a common folk belief in non-Buddhist cultures too; for example:

don't jinx it

• Anyone can explain this expresion to me? and in what context can I use it?

• A jinx is a little like a magical spell, specifically to make something go wrong. It's often used to refer to something good that is hoped will happen, but that might not happen if you talk about it in advance. "Don't jinx it by talking about it."

Or this:

• "How beautiful are the noble children! How large are their eyes! And so young too! Indeed, indeed, I might have remembered that the children of kings are men from the beginning."

• Now, Tabaqui knew as well as anyone else that there is nothing so unlucky as to compliment children to their faces. It pleased him to see (the parents) look uncomfortable.

Or I can think of many other examples.

One possible (non-supernatural) explanation might be that things are likely to get "better" or "worse" by themselves, no matter what anyone says -- and anyone expecting a "good" state to continue might be mistaken.

For example, I once read another (non-Buddhism) aphorism, "good health is a temporary state which foretells nothing good" -- and I read something similar last night, though I forget where: the young Buddha telling an old man that only a fool would see their body as healthy.

A corollary might be that it's better might be that it's better not to say such things (i.e. if it's customary not to say such things then maybe this is one of the reasons for the custom). For example there's this story (which is maybe Zen or more possibly Taoist), about how it's wrong to predict the future (and predictions are often wrong).

Anther practical reason might be found in the (again, non-Buddhist) phrase: "Hope for the best but plan for the worst." If you're not aware of the possibility that things might (or will) go 'bad' then you have no plan to handle it or you're slow to recognize the need for that plan and put it into action.

Saying such a thing (e.g. "he is winning") might show an attachment to that thing (attachment to "his state-of-winning").

“aswaha” and “katawah” in Sinhala, if translated could be said as “Evil eye, evil mouth and evil tongue”. This belief is found in almost all cultures. The effect of the evil eye is being misfortunate. The same is true in Buddhism. This is something that comes to pass when one tries to put into practice the Dhamma that one has learnt. This person could be one who has cultivated the five ‘Sēkha Bala Dhamma’ – Saddhā (faith), Sīla (virtue), Sutha (Dhamma knowledge), Thyāga (generosity), and Paññā (wisdom of the Dhamma). Also this could be a person that has religiously gone through the stages of listening, remembering, constant reciting, mental observation and ideologically understanding the Dhamma (Sutha, dhata, vacasa paricita, manasanupekkhita, ditthiya suppatividdha). Still when trying to put into practice in daily life, what one has learnt, one faces many obstacles, difficulties, emotional pain, and conflicts that throw one away from this Dhamma path. This is due to the “Evil eye, evil mouth and evil tongue” of ones own making.

We’ve got to remember that Mara has a stranglehold of our six senses. (Mara is more precisely understood as "cravings and delusions") In the Samyutta Nikāya 4 -Connected Discourses with Mara: 19 – The Farmer this point is made clear to us.

“Mine alone is the eye (in creatures). Mine are forms, mine is the sphere of consciousness & contact at the eye. Where can you go to escape me? Mine alone is the ear…the nose…the tongue…the body…. Mine alone is the intellect. Mine are ideas, mine is the sphere of consciousness & contact at the intellect. Where can you go to escape me?” – Mara

“Yours alone is the eye, Evil One. Yours are forms, yours is the sphere of consciousness of contact at the eye. Where no eye exists, no forms exist, no sphere of consciousness & contact at the eye exists: there, Evil One, you cannot go. Yours alone is the ear…the nose…the tongue…the body…. Yours alone is the intellect, Evil One. Yours are ideas, yours is the sphere of consciousness & contact at the intellect. Where no intellect exists, no ideas exist, no sphere of consciousness of contact at the intellect exists: there, Evil One, you cannot go.” – Buddha

Remember well the Supreme Buddha’s words…

“Dear Bhikkhus, ones who would not realize this Dhamma is like this earth (in amount). Ones who realize the Nibbāna is like this small amount of soil on my finger nail.”

The “Lokavidu” Buddha, the ‘knower of the worlds’ showed us the path, and told us how to escape from all the worlds. This Dhamma is for the wise. Each one has to come to Dhamma by one’s own effort. As it is to be personally known by the wise, one cannot force it on ones loved one. The Dhamma can be perfectly realized only by the noble disciples (Ariyas) who have matured and enlightened enough in supreme wisdom. So as long as we keep our personal practice very close to our hearts, with utmost humility, one can go far in this path.

There is possibility of being one amongst the minute few who remain in the finger tip, if we could relegate self, and put Dhamma to the forefront. This is an extremely difficult thing to do. That is why only a minute few succeed in this Path. If you are of the “I think therefore I am” type, telling the whole wide world what you do, why and how you go about it, you will not gain anything in this path even if you meditate at length, and you are the most benevolent, righteous person as per world view.