We don´t say mutluca geldi or güzelce þarký söyledi, we always use mutlu bir þekilde geldi and güzel bir þekilde þarký söyledi..

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:"Times New Roman"; color:maroon; font-weight:bold; mso-bidi-font-weight:normal;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 70.85pt 70.85pt 70.85pt; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> I don´t see anything wrong with mutluca geldi or güzelce þarký söyledi. They are correct. They can be used.

We use it for adj. when we believe that quality is close to the said adj.

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:"Times New Roman"; color:maroon; font-weight:bold; mso-bidi-font-weight:normal;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 70.85pt 70.85pt 70.85pt; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> -ce suffix also makes adverbs

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:"Times New Roman"; color:maroon; font-weight:bold; mso-bidi-font-weight:normal;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 70.85pt 70.85pt 70.85pt; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Çabukça eve geldi

Hýzlýca soludu

Yavaþça sývýþtý

Güzelce dinlendi

Ýyice emin oldu

etc

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:"Times New Roman"; color:maroon; font-weight:bold; mso-bidi-font-weight:normal;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 70.85pt 70.85pt 70.85pt; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> 

slightly beautiful / so so girl (not very beautiful, but not ugly) - güzelce bir kýz

slightly fat man - þiþmanca bir adam..

a bit saddish expression - üzgünce bir ifade

a plate larger than usual - büyükçe bir tabak

But it is not very common to use it with adj, unless you want to mean it.  I hope this makes it clear.

What is this admin? My post has been screwed up.

 That is really funny...

 The fact that his post was screwed up or do you mean that what si++ says is wrong?  

 Could you tell me when did you in your life used it like: mutluca geldi, or güzelce þarký söyledi... may be it is not wrong grammatically, <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:"Times New Roman"; color:maroon; font-weight:bold; mso-bidi-font-weight:normal;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 70.85pt 70.85pt 70.85pt; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> OK you accept it they are not wrong, so they can be used. They sound OK to me when somebody says ´em. but we never use it..

The other examples you have given can not apply for other adjectives as these ones are always used like that...

hýzlýca solumak

iyice emin olmak

yavaþça sývýþmak

güzelce dinlenmek

as using them like:

iyi bir þekilde emin olmak

yavaþ bir þekilde dinlenmek

güzel bir þekilde dinlenmek

hýzli bir þekilde solumak

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:"Times New Roman"; color:maroon; font-weight:bold; mso-bidi-font-weight:normal;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 70.85pt 70.85pt 70.85pt; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> I would prefer the shorter ones and they give the same meaning to me. Usually shorter forms are preferred. It´s human nature to choose the shorter forms and seen in every language.

does not give the same meaning, and is not used widely.

 i think there is some kind of conspiracy to your posts..

Please keep conspiracy theories out of the Language Section - and in General/Offtopic where they belong!! 

Please keep conspiracy theories out of the Language Section - and in General/Offtopic where they belong!! 

 It´s not fair.. we were just joking