Fluent interactive conversation usually owes more to rapid short phrases than to long complex sentences. If you can have a few dozen of these phrases firmly in your head, ready for use, you should find the wheels turning more easily when you engage in dialogue with others.
The phrases might appear more formally in a written text. Here they are given in an idiomatic spoken register. Colloquially, it is also possible to replace particle ny / nynj with particle na / nag.
[A] wosta
You know (filler)
An very poynt y honen
That’s just the point
Anhegol dell ...
It’s incredible that ...
Anodho ny’m deur
That doesn’t concern me
Assentys
I agree
Bëdh sur
Rest assured
Bohes lycklod
Not likely
Bÿth na lavar a’n dra
Don’t mention it
Cales yw assentya
It’s hard to agree with that
Cudyn vëth
No problem
Dell leverys
As I said
Der dal consydra
It’s worth bearing in mind
Der dyba’
I think
I suppose
Der gresa'
I believe
Der hevel
Apparently
Der hevel dhèm
I think
I believe
Der ruga soposya
As I thought
Der ruga tyby
As I thought
Der vadna’ brusy
If you ask me
Der welama vy
As I see it
Der wodher
Of course
Desevos dr'yw
I assume
Dhe dhyspûtya martesen
Well I don’t know about that
Dhe’m breus vy
In my opinion
Dhe’m tybyans vy
To my way of thinking
Dhe’m dese'vy
I assume
Dhe’m golok vy
As I see it
Dhe’m govenek vy
I hope
Dhe'm govenek gwir
Let’s hope so
Dowt a'm beus na vo gwir
I rather doubt it
Dowt vëth
No doubt
Don’t worry (expressing certainty)
Dr'ero'vy qweles an dra
As I see it (playing for time)
Dr'yw apert
Evidently
Obviously
Dr'yw dhe wetyas
I expect
Dr'yw gàs plesour
As you like
Dr'yw meur dhe les
That's interesting
Dr'yw ôpynwelys
As anyone can see
[Dr'yw] res alowa
I must admit
You must admit
Eâ
Yes
Er y wu
Unfortunately
Worse luck
Flows
Nonsense
Flows ha whedhlow
Rubbish
Furneth yw hedna
That’s a good point
Gas ny dhe weles
Let’s see
We’ll have to see
Ges a wrêta
You’re joking
Ges vëth
Seriously
No kidding
Goda chauns re’th fo
Good luck with that
Govenek dr'eus dhèm
I hope so
Govyn y hyller dâ
One might well ask
Gwir glân
That’s right
Gwir poran
That’s quite right
Gwir yn tien
That’s quite right
G'ra pêsya
Go on
Gwydn ow bÿs
I’m delighted
Ha ny o'cowsa
By the way
Ha ny o'cows a'n dra
And while we’re on that
Heb bos gwir poran
Not exactly
Heb bos res porrês
Not necessarily
Heb mar
Of course
Certainly
Hèn yw dhe lawl
I mean
Hèn yw lowr
Enough of that
Hèn yw onen dâ
You must be joking
I’n gwelha prës
Fortunately
I’n gwetha prës
Unfortunately
In neb vorr lawl
In a manner of speaking
Kê wàr dha gàm
Steady on
Not so fast
Ken breus a'm beus
I disagree
I see it differently
Lawl der rug vy kyns
As I’ve said before
Lawl der rug vy namnygen
As I’ve just said
Lyckly lowr
Probably
Quite likely
Martesen / martessen
Perhaps
Maybe
I suppose so (when implicitly disagreeing)
Nâ
No
Na fors
Never mind
Naneyl obma nag ena
That’s not the point
Neb gradh
Up to a point
Neb styr
In a sense
Nor'vy màn
I haven’t the faintest idea
How should I know?
Nor'vy ùnderstondya
I don't understand
Ny’m deur
I don’t care
Ny rov oy a hedna
I’m not bothered about that
Ny vern
It doesn’t matter
Ny wora' convedhes
I don’t get it
Nynj erom o'cachya dha styr
I don’t quite get your point
Nynj om’ assentys
I disagree
Nynj oma sur
I’m not sure
Nynj yw badna perthynus
That’s got nothing to do with it
Nynj yw marth
No wonder
Ogh, tybys ken oma vy
Oh, I wouldn't say that (mildly protesting disagreement)
Osta sad?
Are you serious? (as exclamation)
Ot an dra
The question is
Ow styr yw hebma
What I mean is
Pëth a vynta lawl?
What do you mean?
Pòr wir
That’s right
Pùb lycklod
I dare say
Qwestyon dâ
Good question
I wonder
Rag cows dhe blebmyk
Frankly
To be honest
Re’m fay
Well I never
Ren ow thas
Gosh
Good grief
Ria reva
Wow
Scant ny vëdh lyckly
That's hardly likely
Scant y fia marth
I shouldn’t be surprised
Scant yw marth
It’s hardly surprising
Soweth
Unfortunately
More’s the pity
Sur
Of course
Th’erom’ in nevow
I couldn’t be happier
Tra sur
Sure thing
Tra vëth ny vern
It really doesn’t matter
Tybyans dâ
Good idea
Good thinking
Ùnpossybyl
Impossible
Out of the question
Unver oll
I totally agree with you
Unweyth arta mar pleg
Could you repeat that please?
Wàr an tu / tenewen aral
On the other hand
Wèl mara’ teur
Well if you’re interested
Wèl otta sy
Well there you are
Yn tefry
Indeed
Yn tien
Absolutely