Translation of the plugin

Seems author is not here. May be somebody else could help me?

I inserted the following code into my functions.php

//Filters "post of part of the series: " text

function translate_series_content() {echo ("Эта статья является частью серии:");}
add_filter ('post-series-manager-series-text','translate_series_content');

// Filters the "Other posts in this series:" text
function translate_series_other() {echo ("Другие статьи серии:");}
add_filter ('post-series-list-intro-text','translate_series_other');

// Filters the "Continue reading this series:" text
function translate_series_next() {echo ("Следующая статья серии:");}
add_filter ('post-series-manager-next-text','translate_series_next');

But now all the translation texts are printed in the beginning of a post, and the links start next line. I had to insert remove filter to block “after” links, otherwise translation is in the beginning, and links is below the post.

// Remove the shortcode that's automatically added before the content
//remove_filter( 'the_content', array( $post_series_manager, 'post_series_before' ) );
// Remove the shortcode that's automatically added after the content
remove_filter( 'the_content', array( $post_series_manager, 'post_series_after' ) );

I am new to WP and I am not a coder. Where are my mistakes?