Magento2: How to translate search box input field

Question

How can I translate text in i18n Enter keywords to search...shows in this way? I add to file translate: "Enter keywords to search...","Szukaj produktu" but no result.

<input id="search"
                       data-mage-init='{"quickSearch":{
                            "formSelector":"#search_mini_form",
                            "url":"<?php /* @escapeNotVerified */
                       echo $block->getUrl('search/ajax/suggest'); ?>",
                            "destinationSelector":"#search_autocomplete"}
                       }'
                       type="text"
                       name="<?php /* @escapeNotVerified */
                       echo $helper->getQueryParamName() ?>"
                       onfocus="if(this.value=='Enter keywords to search...') this.value='';"
                       onblur="if(this.value=='') this.value='Enter keywords to search...';"
                       value="Enter keywords to search..."
                       class="input-text"
                       maxlength="<?php /* @escapeNotVerified */
                       echo $helper->getMaxQueryLength(); ?>"
                       role="combobox"
                       aria-haspopup="false"
                       aria-autocomplete="both"
                       autocomplete="off"/>

Answer 1

You are missing the PHP translate function :

...
onfocus="if(this.value=='<?= __("Enter keywords to search...") ?>') this.value='';"
onblur="if(this.value=='') this.value='<?= __("Enter keywords to search...") ?>';"
value="<?= __("Enter keywords to search...") ?>"
...

Then, you can clear your Magento Cache, or do a php bin/magento setup:upgrade in ssh console.