Though translation is out of scope, I thought that I as a Polish speaker might help. Marthaª and PLL are both correct as far as they go.

The original poem by Szymborska has (including the lines immediately preceding and following):

obwód w biodrach dwa palce szarada i szyfr,
w którym słowiczku mój a leć, a piej
oraz uprasza się zachować spokój,

Literally translated, this would be

hip measurement two fingers charade and cipher,
in which my dear-little-nightingale fly and sing
and are advised to remain peaceful

(Where "dear-little-nightingale" represents my crude attempt at the Polish słowiczku, a diminutive of słowik, nightingale.)

A person well-read in Polish would know immediately that this a direct quotation from the poem "Do Bohdana Zaleskiego" by Adam Mickiewicz, Poland's greatest poet. It was written in 1841 and uses rather old-fashioned but evocative language.

Słowiczku mój! a leć! a piej!
Na pożegnanie piej
Wylanym łzom, spełnionym snom,
Skończonej piosnce twej!

or

My dear nightingale! Fly! Sing!
In farewell sing
Outpoured tears, fulfilled dreams,
Your finished song!

I do not know the exact intent of the poet, but it was written during the Great Polish Emigration to the west of Europe, a time of tremendous artistic and cultural growth for Poles (think Chopin and Curie) despite their lack of an independent nation. Therefore, its import is somewhat 'patriotic', though in a uniquely Polish sense. The phrase is therefore a classic line by a very famous poet about a joyous bird. The translation mentioned in Marthaª's answer used an equivalent classic English poetic line by Shelley and really did a good job in my opinion.

(The next line is also a bit of a quotation, but for the common phrase "Please remain calm".)

Regarding "blithe" and "trostle":

I can only suspect that the translator who used "trostle" was looking for an antique-feeling equivalent to "nightingale" since the Polish language was similarly old-fashioned. He may have used "blithe" to evoke the Shelly quote. The original Polish does not specifically refer to "blithe", but the mood of the Polish poem is definitely joyous!

Though translation is out of scope, I thought that I as a Polish speaker might help. Marthaª and PLL are both correct as far as they go.

The original poem by Szymborska has (including the lines immediately preceding and following):

obwód w biodrach dwa palce szarada i szyfr,
w którym słowiczku mój a leć, a piej
oraz uprasza się zachować spokój,

Literally translated, this would be

hip measurement two fingers charade and cipher,
in which my dear-little-nightingale fly and sing
and are advised to remain peaceful

(Where "dear-little-nightingale" represents my crude attempt at the Polish słowiczku, a diminutive of słowik, nightingale.)

A person well-read in Polish would know immediately that this a direct quotation from the poem "Do Bohdana Zaleskiego" by Adam Mickiewicz, Poland's greatest poet. It was written in 1841 and uses rather old-fashioned but evocative language.

Słowiczku mój! a leć! a piej!
Na pożegnanie piej
Wylanym łzom, spełnionym snom,
Skończonej piosnce twej!

or

My dear nightingale! Fly! Sing!
In farewell sing
Outpoured tears, fulfilled dreams,
Your finished song!

I do not know the exact intent of the poet, but it was written during the Great Polish Emigration to the west of Europe, a time of tremendous artistic and cultural growth for Poles (think Chopin and Curie) despite their lack of an independent nation. Therefore, its import is somewhat 'patriotic', though in a uniquely Polish sense. The phrase is therefore a classic line by a very famous poet about a joyous bird. The translation mentioned in Marthaª's answer used an equivalent classic English poetic line by Shelley and really did a good job in my opinion.

(The next line is also a bit of a quotation, but for the common phrase "Please remain calm".)

Regarding "blithe" and "trostle":

I can only suspect that the translator who used "trostle" was looking for an antique-feeling equivalent to "nightingale" since the Polish language of the original is similarly old-fashioned. He may have used "blithe" to evoke the Shelly quote. The original Polish does not specifically refer to "blithe", but the mood of the Polish poem is definitely joyous!

Though translation is out of scope, I thought that I as a Polish speaker might help. Marthaª and PLL are both correct as far as they go.

The original poem by Szymborska has (including the lines immediately preceding and following):

obwód w biodrach dwa palce szarada i szyfr,
w którym słowiczku mój a leć, a piej
oraz uprasza się zachować spokój,

Literally translated, this would be

hip measurement two fingers charade and cipher,
in which my dear-little-nightingale fly and sing
and are advised to remain peaceful

(Where "dear-little-nightingale" represents my crude attempt at the Polish słowiczku, a diminutive of słowik, nightingale.)

A person well-read in Polish would know immediately that this a direct quotation from the poem "Do Bohdana Zaleskiego" by Adam Mickiewicz, Poland's greatest poet. It was written in 1841 and uses rather old-fashioned but evocative language.

Słowiczku mój! a leć! a piej!
Na pożegnanie piej
Wylanym łzom, spełnionym snom,
Skończonej piosnce twej!

or

My dear nightingale! Fly! Sing!
In farewell sing
Outpoured tears, fulfilled dreams,
Your finished song!

I do not know the exact intent of the poet, but it was written during the Great Polish Emigration to the west of Europe, a time of tremendous artistic and cultural growth for Poles (think Chopin and Curie) despite their lack of an independent nation. Therefore, its import is somewhat 'patriotic', though in a uniquely Polish sense. The phrase is therefore a classic Polish poetic line. The translation mentioned in Marthaª's answer used an equivalent classic English poetic line by Shelley and really did a good job in my opinion.

(The next line is also a bit of a quotation, but for the common phrase "Please remain calm".)

Though translation is out of scope, I thought that I as a Polish speaker might help. Marthaª and PLL are both correct as far as they go.

The original poem by Szymborska has (including the lines immediately preceding and following):

obwód w biodrach dwa palce szarada i szyfr,
w którym słowiczku mój a leć, a piej
oraz uprasza się zachować spokój,

Literally translated, this would be

hip measurement two fingers charade and cipher,
in which my dear-little-nightingale fly and sing
and are advised to remain peaceful

(Where "dear-little-nightingale" represents my crude attempt at the Polish słowiczku, a diminutive of słowik, nightingale.)

A person well-read in Polish would know immediately that this a direct quotation from the poem "Do Bohdana Zaleskiego" by Adam Mickiewicz, Poland's greatest poet. It was written in 1841 and uses rather old-fashioned but evocative language.

Słowiczku mój! a leć! a piej!
Na pożegnanie piej
Wylanym łzom, spełnionym snom,
Skończonej piosnce twej!

or

My dear nightingale! Fly! Sing!
In farewell sing
Outpoured tears, fulfilled dreams,
Your finished song!

I do not know the exact intent of the poet, but it was written during the Great Polish Emigration to the west of Europe, a time of tremendous artistic and cultural growth for Poles (think Chopin and Curie) despite their lack of an independent nation. Therefore, its import is somewhat 'patriotic', though in a uniquely Polish sense. The phrase is therefore a classic line by a very famous poet about a joyous bird. The translation mentioned in Marthaª's answer used an equivalent classic English poetic line by Shelley and really did a good job in my opinion.

(The next line is also a bit of a quotation, but for the common phrase "Please remain calm".)

Regarding "blithe" and "trostle":

I can only suspect that the translator who used "trostle" was looking for an antique-feeling equivalent to "nightingale" since the Polish language was similarly old-fashioned. He may have used "blithe" to evoke the Shelly quote. The original Polish does not specifically refer to "blithe", but the mood of the Polish poem is definitely joyous!